Peptide core-based multi-arm linkers for treating infectious diseases

ABSTRACT

The present disclosure provides various molecular constructs having a targeting element and an effector element. Methods for treating various diseases using such molecular constructs are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to the field of pharmaceuticals; moreparticularly, to multi-functional molecular constructs, e.g., thosehaving targeting and effector elements for delivering the effector(e.g., therapeutic drug) to targeted sites.

2. Description of the Related Art

The continual advancement of a broad array of methodologies forscreening and selecting monoclonal antibodies (mAbs) for targetedantigens has helped the development of a good number of therapeuticantibodies for many diseases that were regarded as untreatable just afew years ago. According to Therapeutic Antibody Database, approximately2,800 antibodies have been studied or are being planned for studies inhuman clinical trials, and approximately 80 antibodies have beenapproved by governmental drug regulatory agencies for clinical uses. Thelarge amount of data on the therapeutic effects of antibodies hasprovided information concerning the pharmacological mechanisms howantibodies act as therapeutics.

One major pharmacologic mechanism for antibodies acting as therapeuticsis that, antibodies can neutralize or trap disease-causing mediators,which may be cytokines or immune components present in the bloodcirculation, interstitial space, or in the lymph nodes. The neutralizingactivity inhibits the interaction of the disease-causing mediators withtheir receptors. It should be noted that fusion proteins of the solublereceptors or the extracellular portions of receptors of cytokines andthe Fc portion of IgG, which act by neutralizing the cytokines or immunefactors in a similar fashion as neutralizing antibodies, have also beendeveloped as therapeutic agents.

Several therapeutic antibodies that have been approved for clinicalapplications or subjected to clinical developments mediate theirpharmacologic effects by binding to receptors, thereby blocking theinteraction of the receptors with their ligands. For those antibodydrugs, Fc-mediated mechanisms, such as antibody-dependent cellularcytotoxicity (ADCC) and complement-mediated cytolysis (CMC), are not theintended mechanisms for the antibodies.

Some therapeutic antibodies bind to certain surface antigens on targetcells and render Fc-mediated functions and other mechanisms on thetarget cells. The most important Fc-mediated mechanisms areantibody-dependent cellular cytotoxicity (ADCC) and complement-mediatedcytolysis (CMC), which both will cause the lysis of the antibody-boundtarget cells. Some antibodies binding to certain cell surface antigenscan induce apoptosis of the bound target cells.

The concept and methodology for preparing antibodies with dualspecificities germinated more than three decades ago. In recent year,the advancement in recombinant antibody engineering methodologies andthe drive to develop improved medicine has stimulated the developmentbi-specific antibodies adopting a large variety of structuralconfigurations.

For example, the bi-valent or multivalent antibodies may contain two ormore antigen-binding sites. A number of methods have been reported forpreparing multivalent antibodies by covalently linking three or four Fabfragments via a connecting structure. For example, antibodies have beenengineered to express tandem three or four Fab repeats.

Several methods for producing multivalent antibodies by employingsynthetic crosslinkers to associate, chemically, different antibodies orbinding fragments have been disclosed. One approach involves chemicallycross-linking three, four, and more separately Fab fragments usingdifferent linkers. Another method to produce a construct with multipleFabs that are assembled to one-dimensional DNA scaffold was provided.Those various multivalent Ab constructs designed for binding to targetmolecules differ among one another in size, half-lives, flexibility inconformation, and ability to modulate the immune system. In view of theforegoing, several reports have been made for preparing molecularconstructs with a fixed number of effector elements or with two or moredifferent kinds of functional elements (e.g., at least one targetingelement and at least one effector element). However, it is oftendifficult to build a molecular construct with a particular combinationof the targeting and effector elements either using chemical synthesisor recombinant technology. Accordingly, there exists a need in therelated art to provide novel molecular platforms to build a moreversatile molecule suitable for covering applications in a wide range ofdiseases.

SUMMARY

The following presents a simplified summary of the disclosure in orderto provide a basic understanding to the reader. This summary is not anextensive overview of the disclosure and it does not identifykey/critical elements of the present invention or delineate the scope ofthe present invention. Its sole purpose is to present some conceptsdisclosed herein in a simplified form as a prelude to the more detaileddescription that is presented later.

<I> Peptide Core-Based Multi-Arm Linkers

In the first aspect, the present disclosure is directed to a linker unitthat has at least two different functional elements linked thereto. Forexample, the linker unit may have linked thereto two different effectorelements, one targeting element and one effector element, or oneeffector element and a polyethylene glycol (PEG) chain for prolongingthe circulation time of the linker unit. The present linker unit isdesigned to have at least two different functional groups such that thefunctional elements can be linked thereto by reacting with therespective functional groups. Accordingly, the present linker unit canserve as a platform for preparing a molecular construct with two or morefunctional elements.

According to various embodiments of the present disclosure, the linkerunit comprises a center core and a plurality of linking arms. The centercore is a polypeptide core comprising (1) a plurality of lysine (K)resides, in which each K residue and a next K residue are separated by afiller sequence comprising glycine (G) and serine (5) residues, and thenumber of K residues ranges from 2 to 15; or (2) the sequence of(X_(aa)—K)_(n), where X_(aa) is a PEGylated amino acid having 2 to 12repeats of ethylene glycol (EG) unit, and n is an integral from 2 to 15.Optionally, the filler sequence consists of 2 to 20 amino acid residues.In various embodiments, the filler sequence may have the sequence of GS,GGS, GSG, or SEQ ID NOs: 1-16. According to some embodiments of thepresent disclosure, the center core comprises 2-15 units of the sequenceof G₁₋₅SK; preferably, the center core comprises the sequence of(GSK)₂₋₁₅. Each of the linking arms is linked to the K residues of thecenter core via forming an amide linkage between the K residue and thelinking arm. The linking arm linked to the center core has a maleimide,a N-hydroxysuccinimidyl (NHS) group, an azide group, an alkyne group, atetrazine group, a cyclooctene group, or a cyclooctyne group at itsfree-terminus. Also, the amino acid residue at the N- or C-terminus ofthe center core has an azide group or an alkyne group; alternatively oradditionally, the amino acid residue at the N- or C-terminus of thecenter core is a cysteine (C) residue, in which the thiol group of theamino acid residue is linked with a coupling arm having an azide group,an alkyne group, a tetrazine group, a cyclooctene group, or acyclooctyne group at the free terminus of the coupling arm.

According to some embodiments of the present disclosure, when the freeterminus of the linking arm is the azide, the alkyne, or the cyclooctynegroup, then the amino acid residue at the N- or C-terminus of the centercore is a cysteine residue, and the free terminus of the coupling arm isthe tetrazine or the cyclooctene group. According to other embodimentsof the present disclosure, when the free terminus of the linking arm isthe tetrazine group or cyclooctene group, then the amino acid residue atthe N- or C-terminus of the center core has the azide or the alkynegroup, or the amino acid residue at the N- or C-terminus of the centercore is a cysteine residue, and the free terminus of the coupling arm isthe azide, the alkyne, or the cyclooctyne group.

In some embodiments, the linking arm is a PEG chain, preferably having 2to 20 repeats of EG units. Alternatively, the linking arm is a PEG chainhaving 2 to 20 repeats of EG units with a disulfide linkage at the freeterminus thereof (i.e., the terminus that is not linked with the Kresidue of the center core). In some embodiments, the coupling linkingarm is a PEG chain, preferably having 2 to 12 repeats of EG units.

Regarding amino acid residues having the azide group, non-limitingexamples of said amino acid residues include L-azidohomoalanine (AHA),4-azido-L-phenylalanine, 4-azido-D-phenylalanine, 3-azido-L-alanine,3-azido-D-alanine, 4-azido-L-homoalanine, 4-azido-D-homoalanine,5-azido-L-ornithine, 5-azido-d-ornithine, 6-azido-L-lysine, and6-azido-D-lysine. As to the amino acid residues having the alkyne group,illustrative examples thereof include L-homopropargylglycine (L-HPG),D-homopropargylglycine (D-HPG), and beta-homopropargylglycine (β-HPG).

When the amino acid residues at the N- or C-terminus of the center coreis the cysteine residue, the cyclooctene group at the free terminus ofthe coupling arm may be, a trans-cyclooctene (TCO) group, while thecyclooctyne group at the free terminus of the coupling arm may be adibenzocyclooctyne (DBCO), difluorinated cyclooctyne (DIFO),bicyclononyne (BCN), or dibenzocyclooctyne (DICO) group. Alternatively,the tetrazine group at the free terminus of the coupling arm includes,but is not limited to, 1,2,3,4-tetrazine, 1,2,3,5-tetrazine, and1,2,4,5-tetrazine, and derivatives thereof, such as, 6-methyl tetrazine.

According to various embodiments of the present disclosure, the linkerunit further comprises a plurality of first elements. In someembodiments, each of the first elements is linked to one of the linkingarms via forming an amide bound between the linking arm and the firstelement. In other embodiments, each of the first elements is linked toone of the linking arms via copper catalyzed azide-alkyne cycloaddition(CuAAC) reaction, strained-promoted azide-alkyne click chemistry (SPAAC)reaction, or inverse electron demand Diels-Alder (iEDDA) reactionoccurred between the linking arm and the first element.

Optionally, the present linker unit further comprises a plurality ofconnecting arms that are respectively linked to the plurality of linkingarms via CuAAC reaction, SPAAC reaction, or iEDDA reaction. According tothe embodiments of the present disclosure, each of the plurality ofconnecting arms has a maleimide or the NHS group at the element-linkingterminus thereof (i.e., the terminus that is not linked with the linkingarm). Accordingly, each of the first elements is linked to one of theconnecting arms via the thiol-maleimide reaction occurred between theconnecting arm and the first element; or each of the first elements islinked to one of the connecting arms via forming an amide bound betweenthe connecting arm and the first element. In some embodiments, each ofthe connecting arms is a PEG chain, preferably having 2-20 repeats of EGunits. In other embodiments, each of the connecting arms is a PEG chainhaving 2-20 repeats of EG units with a disulfide linkage at theelement-linking terminus.

According to various optional embodiments of the present disclosure, thefirst element is an effector element suitable for eliciting an intendedeffect (e.g., a therapeutic effect) in a subject. Alternatively, thefirst element may be a targeting element for directing the linker unitto the site of interest. According to the embodiments of the presentdisclosure, the first element is fingolimod, fingolimod phosphate,interferon-β, or a single-chain variable fragment (scFv) specific forintegrin-α4, β-amyloid, a viral protein, a bacterial protein.

Still optionally, the linker unit further comprises a second elementthat is different from the first elements. In some embodiments, thesecond element has an azide or alkyne group, so that it is linked to thecenter core or the coupling arm by coupling with the correspondingalkyne or azide group of the center core or the coupling arm via CuAACreaction. Alternatively, in some embodiments, the second element havingan azide or cyclooctyne group is linked to the center core or thecoupling arm by coupling with the corresponding cyclooctyne or azidegroup of the center core or the coupling arm via SPAAC reaction. Stillalternatively, in certain embodiments, the second element having atetrazine or cyclooctene group is linked to the center core or thecoupling arm by coupling with the corresponding cyclooctene or tetrazinegroup of the center core or the coupling arm via iEDDA) reaction.According to some embodiments, the linker unit comprises the connectingarm, which is linked to the linking arm via CuAAC reaction or SPAACreaction; in these embodiments, the N- or C-terminus of the center coreor the free terminus of the coupling arm has a tetrazine or cyclooctenegroup so that the second element having the corresponding cyclooctene ortetrazine group is linked to the center core or the coupling arm viaiEDDA reaction. According to other embodiments, the linker unitcomprises the connecting arm, which is linked to the linking arm viaiEDDA reaction; in these conditions, the N- or C-terminus of the centercore or the free terminus of the coupling arm has an azide, alkyne, orcyclooctyne group so that the second element having the correspondingchemical groups is linked to the center core or the coupling arm viaCuAAC reaction or SPAAC reaction.

In optional embodiments of the present disclosure, when the firstelement is an effector element, then the second element may be anothereffector element, which works additively or synergistically with orindependently of the first element; alternatively, the second elementmay be a targeting element or an element for improving thepharmacokinetic property of the linker unit, such as solubility,clearance, half-life, and bioavailability. In some other optionalembodiments, when the first element is the targeting element, then thesecond element is preferably an effector element or an element forimproving the pharmacokinetic property of the linker unit.

In certain embodiments, the linker unit further comprises an optionalthird element that is different from the first and second elements. Inthe case where the second element is directly linked to the center core,the other terminus (i.e., the free terminus that is not linked with thesecond element) of the center core is optionally a cysteine residue,which can be used to introduce an optional third element. Specifically,the thiol group of the cysteine residue is reacted with a maleimidegroup of a PEG chain; and the thus-linked PEG chain is designated as thecoupling arm, which has a tetrazine group or a cyclooctene group at itsfree terminus. Accordingly, the third element is then linked to thecoupling arm via iEDDA reaction. In the case where the linker unitcomprises both the second and third elements, it is preferable that atleast one of the first and second elements is an effector as describedabove, while the third element may be the element for improving thepharmacokinetic property of the linker unit. One example of the elementfor improving the pharmacokinetic property is a long PEG chain having amolecular weight of about 20,000 to 50,000 daltons.

<II> Uses of Peptide Core-Based Multi-Arm Linkers

The linker unit according to the first aspect of the present disclosuremay find its utility in clinical medicine for the treatment of variousdiseases. Hence, the second aspect of the present disclosure is directedto a method for treating these diseases. According to variousembodiments of the present disclosure, the method for treating aparticular disease includes the step of administering to the subject inneed thereof a therapeutically effective amount of the linker unitaccording to the above-mentioned aspect and embodiments of the presentdisclosure. As could be appreciated, said linker unit may beadministered in a pharmaceutical formulation, which comprises apharmaceutically-acceptable excipient suitable for the intended ordesired administration route, in addition to the present linker unit.

Various illustrative combinations of the first and second elements ofthe present linker unit for treating some particular diseases aredisclosed below for facilitating the understanding of some embodimentsof the present disclosure.

According to some embodiments of the present disclosure, the presentlinker unit is useful in treating a central nervous system (CNS)disease, for example, multiple sclerosis and Alzheimer's disease. Forthe treatment of multiple sclerosis, the first element can befingolimod, fingolimod phosphate, interferon-β, or an scFv specific forintegrin-α4. For the purpose of treating Alzheimer's disease, theelement is an scFv specific for β-amyloid.

According to other embodiments of the present disclosure, the linkerunits suitable for treating an infectious disease comprise an scFvspecific for a viral protein or a bacterial protein as the firstelement. In one preferred embodiment, the viral protein is F protein ofrespiratory syncytia virus (RSV), gp120 protein of human deficiencyvirus type 1 (HIV-1), hemagglutinin A (HA) protein of influenza A virus,or glycoprotein of cytomegalovirus; and the bacterial protein isendotoxin of Gram(−) bacteria, surface antigen of Clostridium difficile,lipoteichoic acid of Staphylococcus aureus, anthrax toxin of Bacillusanthracis, or Shiga-like toxin type I or II of Escherichia coli.

BRIEF DESCRIPTION OF THE DRAWINGS

The present description will be better understood from the followingdetailed description read in light of the accompanying drawings brieflydiscussed below.

FIG. 1A to FIG. 1N are schematic diagrams illustrating linker unitsaccording to certain embodiments of the present disclosure.

FIG. 2 shows the mass spectrometry MALDI-TOF result of a peptidecore-based linker-unit carrying one linking arm with tetrazine group andthree PEG linking arms with maleimide groups.

FIG. 3 shows the mass spectrometry MALDI-TOF result ofNHS-PEG₅-conjugated fingolimod.

FIG. 4 shows the mass spectrometry MALDI-TOF result of a drug bundlecomposing of a linker unit with a free TCO functional group and a set of5 fingolimod molecules.

FIG. 5 shows the mass spectrometry MALDI-TOF result of a drug bundlecomposing of a linker unit with a free TOO functional group and a set of10 fingolimod molecules.

FIG. 6 shows the mass spectrometry MALDI-TOF result of a drug bundlecomposing of a linker unit with a free TCO functional group and a set offive fingolimod phosphate molecules.

FIG. 7 shows the SDS-PAGE analysis result of the purified ectodomain ofhuman CD32a.

FIG. 8 shows the SDS-PAGE analysis result of the purified ectodomain ofhuman TfR1.

FIG. 9A shows the SDS-PAGE analysis result of the purified scFv specificfor Protein F of RSV; FIG. 9B shows the ELISA analysis result of thepurified scFv specific for Protein F of RSV; FIG. 9C shows the SDS-PAGEanalysis result of the purified scFv specific for endotoxin; FIG. 9Dshows the ELISA analysis of the purified scFv specific for endotoxin;FIG. 9E shows the SDS-PAGE analysis result of the purified scFv specificfor the ectodomain of CD32a; and FIG. 9F shows the ELISA analysis of thepurified scFv specific for the ectodomain of CD32a.

FIG. 10A shows the SDS-PAGE analysis result of the purified scFvspecific for the ectodomain of rat TfR1; FIG. 10B shows the ELISAanalysis result of the purified scFv specific for the ectodomain of ratTfR1; FIG. 10C shows the SDS-PAGE analysis result of the purified scFvspecific for β-amyloid; and FIG. 10D shows the ELISA analysis of thepurified scFv specific for β-amyloid.

FIG. 11A shows the data of the titers of the phages bearing scFvsspecific for ectodomain of human CD32a; and FIG. 11B shows the singlecolony ELISA analysis result of phage-displayed scFvs specific for theectodomain of human CD32a.

FIG. 12A shows the data of the titers of the phages bearing scFvsspecific for ectodomain of human TfR1; and FIG. 12B shows the singlecolony ELISA analysis of phage-displayed scFvs specific for theectodomain of human TfR1.

FIG. 13A and FIG. 13B respectively show the results of ELISA analysisand mass spectrometric analysis of TCO-conjugated scFv specific forCD32a.

FIG. 14A and FIG. 14B respectively show the results of ELISA analysisand mass spectrometric analysis of tetrazine-conjugated scFv specificfor TfR1.

FIG. 15A shows the FPLC elution profile of size-exclusion column S75 onthe synthesized targeting linker unit composed of a linker unit with afree tetrazine functional group and a set of three scFvs specific forendotoxin as targeting elements; FIG. 15B and FIG. 15C respectively showthe results of the SDS-PAGE analysis result and the ELISA result of thesynthesized targeting linker unit of FIG. 15A.

FIG. 16 shows the mass spectrometric analysis result of the synthesizedtargeting linker unit that was composed of a linker unit with a freetetrazine functional group and a set of three scFv specific for ProteinF of RSV as targeting elements.

FIG. 17A shows the FPLC elution profile of cation ion exchange column ona synthesized targeting linker unit composed of a linker unit with afree TCO functional group and a set of three scFvs specific forβ-amyloid as targeting elements; FIG. 17B and FIG. 170 respectively showthe results of the SDS-PAGE analysis result and the ELISA result of thesynthesized targeting linker unit of FIG. 17A.

FIG. 18A shows the mass spectrometric analysis result of a single linkerunit molecular construct with three scFvs specific for endotoxin astargeting elements and one scFv specific for ectodomain of CD32a as aneffector element; FIG. 18B shows the mass spectrometric analysis resultof a single linker unit molecular construct with three scFvs specificfor endotoxin as targeting elements and one scFv specific for ectodomainof CD32a as an effector element; and FIG. 18C shows the massspectrometric analysis result of a single linker unit molecularconstruct with one scFv specific for ectodomain of TfR1 as a targetingelement and three scFvs specific for β-amyloid as effector elements.

In accordance with common practice, the various describedfeatures/elements are not drawn to scale but instead are drawn to bestillustrate specific features/elements relevant to the present invention.Also, like reference numerals and designations in the various drawingsare used to indicate like elements/parts, where possible.

DESCRIPTION

The detailed description provided below in connection with the appendeddrawings is intended as a description of the present examples and is notintended to represent the only forms in which the present example may beconstructed or utilized. The description sets forth the functions of theexample and the sequence of steps for constructing and operating theexample. However, the same or equivalent functions and sequences may beaccomplished by different examples.

For convenience, certain terms employed in the specification, examplesand appended claims are collected here. Unless otherwise defined herein,scientific and technical terminologies employed in the presentdisclosure shall have the meanings that are commonly understood and usedby one of ordinary skill in the art.

Unless otherwise required by context, it will be understood thatsingular terms shall include plural forms of the same and plural termsshall include the singular. Specifically, as used herein and in theclaims, the singular forms “a” and “an” include the plural referenceunless the context clearly indicated otherwise. Also, as used herein andin the claims, the terms “at least one” and “one or more” have the samemeaning and include one, two, three, or more. Furthermore, the phrases“at least one of A, B, and C”, “at least one of A, B, or C” and “atleast one of A, B and/or C,” as use throughout this specification andthe appended claims, are intended to cover A alone, B alone, C alone, Aand B together, B and C together, A and C together, as well as A, B, andC together.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in therespective testing measurements. Also, as used herein, the term “about”generally means within 10%, 5%, 1%, or 0.5% of a given value or range.Alternatively, the term “about” means within an acceptable standarderror of the mean when considered by one of ordinary skill in the art.Other than in the operating/working examples, or unless otherwiseexpressly specified, all of the numerical ranges, amounts, values andpercentages such as those for quantities of materials, durations oftimes, temperatures, operating conditions, ratios of amounts, and thelikes thereof disclosed herein should be understood as modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the present disclosureand attached claims are approximations that can vary as desired. At thevery least, each numerical parameter should at least be construed inlight of the number of reported significant digits and by applyingordinary rounding techniques. Ranges can be expressed herein as from oneendpoint to another endpoint or between two endpoints. All rangesdisclosed herein are inclusive of the endpoints, unless specifiedotherwise.

This present disclosure pertains generally to molecular constructs, inwhich each molecular construct comprises a targeting element (T) and aneffector element (E), and these molecular constructs are sometimesreferred to as “T-E molecules”, “T-E pharmaceuticals” or “T-E drugs” inthis document.

As used herein, the term “targeting element” refers to the portion of amolecular construct that directly or indirectly binds to a target ofinterest (e.g., a receptor on a cell surface or a protein in a tissue)thereby facilitates the transportation of the present molecularconstruct into the interested target. In some example, the targetingelement may direct the molecular construct to the proximity of thetarget cell. In other cases, the targeting element specifically binds toa molecule present on the target cell surface or to a second moleculethat specifically binds a molecule present on the cell surface. In somecases, the targeting element may be internalized along with the presentmolecular construct once it is bound to the interested target, hence isrelocated into the cytosol of the target cell. A targeting element maybe an antibody or a ligand for a cell surface receptor, or it may be amolecule that binds such antibody or ligand, thereby indirectlytargeting the present molecular construct to the target site (e.g., thesurface of the cell of choice). The localization of the effector(therapeutic agent) in the diseased site will be enhanced or favoredwith the present molecular constructs as compared to the therapeuticwithout a targeting function. The localization is a matter of degree orrelative proportion; it is not meant for absolute or total localizationof the effector to the diseased site.

According to the present invention, the term “effector element” refersto the portion of a molecular construct that elicits a biologicalactivity (e.g., inducing immune responses, exerting cytotoxic effectsand the like) or other functional activity (e.g., recruiting otherhapten tagged therapeutic molecules), once the molecular construct isdirected to its target site. The “effect” can be therapeutic ordiagnostic. The effector elements encompass those that bind to cellsand/or extracellular immunoregulatory factors. The effector elementcomprises agents such as proteins, nucleic acids, lipids, carbohydrates,glycopeptides, drug moieties (both small molecule drug and biologics),compounds, elements, and isotopes, and fragments thereof.

Although the terms, first, second, third, etc., may be used herein todescribe various elements, components, regions, and/or sections, theseelements (as well as components, regions, and/or sections) are not to belimited by these terms. Also, the use of such ordinal numbers does notimply a sequence or order unless clearly indicated by the context.Rather, these terms are simply used to distinguish one element fromanother. Thus, a first element, discussed below, could be termed asecond element without departing from the teachings of the exemplaryembodiments.

Here, the terms “link,” “couple,” and “conjugates” are usedinterchangeably to refer to any means of connecting two componentseither via direct linkage or via indirect linkage between twocomponents.

The term “polypeptide” as used herein refers to a polymer having atleast two amino acid residues. Typically, the polypeptide comprisesamino acid residues ranging in length from 2 to about 200 residues;preferably, 2 to 50 residues. Where an amino acid sequence is providedherein, L-, D-, or beta amino acid versions of the sequence are alsocontemplated. Polypeptides also include amino acid polymers in which oneor more amino acid residues are an artificial chemical analogue of acorresponding naturally occurring amino acid, as well as to naturallyoccurring amino acid polymers. In addition, the term applies to aminoacids joined by a peptide linkage or by other, “modified linkages,”e.g., where the peptide bond is replaced by an α-ester, a β-ester, athioamide, phosphoramide, carbomate, hydroxylate, and the like.

In certain embodiments, conservative substitutions of the amino acidscomprising any of the sequences described herein are contemplated. Invarious embodiments, one, two, three, four, or five different residuesare substituted. The term “conservative substitution” is used to reflectamino acid substitutions that do not substantially alter the activity(e.g., biological or functional activity and/or specificity) of themolecule. Typically, conservative amino acid substitutions involvesubstitution one amino acid for another amino acid with similar chemicalproperties (e.g., charge or hydrophobicity). Certain conservativesubstitutions include “analog substitutions” where a standard amino acidis replaced by a non-standard (e.g., rare, synthetic, etc.) amino aciddiffering minimally from the parental residue. Amino acid analogs areconsidered to be derived synthetically from the standard amino acidswithout sufficient change to the structure of the parent, are isomers,or are metabolite precursors.

In certain embodiments, polypeptides comprising at least 80%, preferablyat least 85% or 90%, and more preferably at least 95% or 98% sequenceidentity with any of the sequences described herein are alsocontemplated.

“Percentage (%) amino acid sequence identity” with respect to thepolypeptide sequences identified herein is defined as the percentage ofpolypeptide residues in a candidate sequence that are identical with theamino acid residues in the specific polypeptide sequence, after aligningthe sequences and introducing gaps, if necessary, to achieve the maximumpercent sequence identity, and not considering any conservativesubstitutions as part of the sequence identity. Alignment for purposesof determining percentage sequence identity can be achieved in variousways that are within the skill in the art, for instance, using publiclyavailable computer software such as BLAST, BLAST-2, ALIGN or Megalign(DNASTAR) software. Those skilled in the art can determine appropriateparameters for measuring alignment, including any algorithms needed toachieve maximal alignment over the full length of the sequences beingcompared. For purposes herein, sequence comparison between twopolypeptide sequences was carried out by computer program Blastp(protein-protein BLAST) provided online by Nation Center forBiotechnology Information (NCBI). The percentage amino acid sequenceidentity of a given polypeptide sequence A to a given polypeptidesequence B (which can alternatively be phrased as a given polypeptidesequence A that has a certain % amino acid sequence identity to a givenpolypeptide sequence B) is calculated by the formula as follows:

$\frac{X}{Y} \times 100\%$

where X is the number of amino acid residues scored as identical matchesby the sequence alignment program BLAST in that program's alignment of Aand B, and where Y is the total number of amino acid residues in A or B,whichever is shorter.

The term “PEGylated amino acid” as used herein refers to a polyethyleneglycol (PEG) chain with one amino group and one carboxyl group.Generally, the PEGylated amino acid has the formula ofNH₂—(CH₂CH₂O)_(n)—COOH. In the present disclosure, the value of n rangesfrom 1 to 20; preferably, ranging from 2 to 12.

As used herein, the term “terminus” with respect to a polypeptide refersto an amino acid residue at the N- or C-end of the polypeptide. Withregard to a polymer, the term “terminus” refers to a constitutional unitof the polymer (e.g., the polyethylene glycol of the present disclosure)that is positioned at the end of the polymeric backbone. In the presentspecification and claims, the term “free terminus” is used to mean theterminal amino acid residue or constitutional unit is not chemicallybound to any other molecular.

The term “antigen” or “Ag” as used herein is defined as a molecule thatelicits an immune response. This immune response may involve asecretory, humoral and/or cellular antigen-specific response. In thepresent disclosure, the term “antigen” can be any of a protein, apolypeptide (including mutants or biologically active fragmentsthereof), a polysaccharide, a glycoprotein, a glycolipid, a nucleicacid, or a combination thereof.

In the present specification and claims, the term “antibody” is used inthe broadest sense and covers fully assembled antibodies, antibodyfragments that bind with antigens, such as antigen-binding fragment(Fab/Fab′), F(ab′)₂ fragment (having two antigen-binding Fab portionslinked together by disulfide bonds), variable fragment (Fv), singlechain variable fragment (scFv), bi-specific single-chain variablefragment (bi-scFv), nanobodies, unibodies and diabodies. “Antibodyfragments” comprise a portion of an intact antibody, preferably theantigen-binding region or variable region of the intact antibody.Typically, an “antibody” refers to a protein consisting of one or morepolypeptides substantially encoded by immunoglobulin genes or fragmentsof immunoglobulin genes. The well-known immunoglobulin genes include thekappa, lambda, alpha, gamma, delta, epsilon, and mu constant regiongenes, as well as myriad immunoglobulin variable region genes. Lightchains are classified as either kappa or lambda. Heavy chains areclassified as gamma, mu, alpha, delta, or epsilon, which in turn definethe immunoglobulin classes, IgG, IgM, IgA, IgD, and IgE, respectively. Atypical immunoglobulin (antibody) structural unit is known to comprise atetramer. Each tetramer is composed of two identical pairs ofpolypeptide chains, with each pair having one “light” chain (about 25kDa) and one “heavy” chain (about 50-70 kDa). The N-terminus of eachchain defines a variable region of about 100 to 110 or more amino acidsprimarily responsible for antigen recognition. The terms variable lightchain (V_(L)) and variable heavy chain (V_(H)) refer to these light andheavy chains, respectively. According to embodiments of the presentdisclosure, the antibody fragment can be produced by modifying thenature antibody or by de novo synthesis using recombinant DNAmethodologies. In certain embodiments of the present disclosure, theantibody and/or antibody fragment can be bispecific, and can be invarious configurations. For example, bispecific antibodies may comprisetwo different antigen binding sites (variable regions). In variousembodiments, bispecific antibodies can be produced by hybridomatechnique or recombinant DNA technique. In certain embodiments,bispecific antibodies have binding specificities for at least twodifferent epitopes.

The term “specifically binds” as used herein, refers to the ability ofan antibody or an antigen-binding fragment thereof, to bind to anantigen with a dissociation constant (Kd) of no more than about 1×10⁻⁶M, 1×10⁻⁷ M, 1×10⁻⁸ M, 1×10⁻⁹ M, 1×10⁻¹⁰ M, 1×10⁻¹¹ M, 1×10⁻¹² M, and/orto bind to an antigen with an affinity that is at least two-foldsgreater than its affinity to a nonspecific antigen.

The term “treatment” as used herein includes preventative (e.g.,prophylactic), curative or palliative treatment; and “treating” as usedherein also includes preventative (e.g., prophylactic), curative orpalliative treatment. In particular, the term “treating” as used hereinrefers to the application or administration of the present molecularconstruct or a pharmaceutical composition comprising the same to asubject, who has a medical condition a symptom associated with themedical condition, a disease or disorder secondary to the medicalcondition, or a predisposition toward the medical condition, with thepurpose to partially or completely alleviate, ameliorate, relieve, delayonset of, inhibit progression of, reduce severity of, and/or reduceincidence of one or more symptoms or features of said particulardisease, disorder, and/or condition. Treatment may be administered to asubject who does not exhibit signs of a disease, disorder, and/orcondition, and/or to a subject who exhibits only early signs of adisease, disorder and/or condition, for the purpose of decreasing therisk of developing pathology associated with the disease, disorderand/or condition.

The term “effective amount” as used herein refers to the quantity of thepresent molecular construct that is sufficient to yield a desiredtherapeutic response. An effective amount of an agent is not required tocure a disease or condition but will provide a treatment for a diseaseor condition such that the onset of the disease or condition is delayed,hindered or prevented, or the disease or condition symptoms areameliorated. The effective amount may be divided into one, two, or moredoses in a suitable form to be administered at one, two or more timesthroughout a designated time period. The specific effective orsufficient amount will vary with such factors as particular conditionbeing treated, the physical condition of the patient (e.g., thepatient's body mass, age, or gender), the type of subject being treated,the duration of the treatment, the nature of concurrent therapy (ifany), and the specific formulations employed and the structure of thecompounds or its derivatives. Effective amount may be expressed, forexample, as the total mass of active component (e.g., in grams,milligrams or micrograms) or a ratio of mass of active component to bodymass, e.g., as milligrams per kilogram (mg/kg).

The terms “application” and “administration” are used interchangeablyherein to mean the application of a molecular construct or apharmaceutical composition of the present invention to a subject in needof a treatment thereof.

The terms “subject” and “patient” are used interchangeably herein andare intended to mean an animal including the human species that istreatable by the molecular construct, pharmaceutical composition, and/ormethod of the present invention. The term “subject” or “patient”intended to refer to both the male and female gender unless one genderis specifically indicated. Accordingly, the term “subject” or “patient”comprises any mammal, which may benefit from the treatment method of thepresent disclosure. Examples of a “subject” or “patient” include, butare not limited to, a human, rat, mouse, guinea pig, monkey, pig, goat,cow, horse, dog, cat, bird and fowl. In an exemplary embodiment, thepatient is a human. The term “mammal” refers to all members of the classMammalia, including humans, primates, domestic and farm animals, such asrabbit, pig, sheep, and cattle; as well as zoo, sports or pet animals;and rodents, such as mouse and rat. The term “non-human mammal” refersto all members of the class Mammalis except human.

The present disclosure is based, at least on the construction of the T-Epharmaceuticals that can be delivered to target cells, target tissues ororgans at increased proportions relative to the blood circulation,lymphoid system, and other cells, tissues or organs. When this isachieved, the therapeutic effect of the pharmaceuticals is increased,while the scope and severity of the side effects and toxicity isdecreased. It is also possible that a therapeutic effector isadministered at a lower dosage in the form of a T-E molecule, than in aform without a targeting component. Therefore, the therapeutic effectorcan be administered at lower dosages without losing potency, whilelowering side effects and toxicity.

Diseases that can Benefit from Better Drug Targeting

Drugs used for many diseases can be improved for better efficacy andsafety, if they can be targeted to the disease sites, i.e., if they canbe localized or partitioned to the disease sites more favorably than thenormal tissues or organs. Certain antibody drugs, which targetinfectious microorganisms or their toxic products, can be improved, ifthey are empowered with the ability to recruit immunocytes, whichphagocytose and clear the antibody-bound particles. Following areprimary examples of diseases, in which drugs can be improved if they canbe preferentially distributed to the disease sites or cells or if theycan recruit phagocytic immunocytes.

I Central Nervous System Diseases

For treating diseases of the central nervous system (CNS), thetherapeutic agents are often required to pass through the blood-brainbarrier (BBB) to get into the CNS. Some therapeutic agents do not getinto the CNS; they regulate certain activities, such as immuneactivities, in the peripheral, which then modulates the diseasedconditions in the CNS. The BBB is formed by the endothelial cells liningthe capillaries of blood vessels in the CNS. Unlike the capillaries inthe peripheral tissues and organs, the capillary endothelial cells inthe BBB are connected by tight junctions formed by occludin, claudins,and junctional adhesion molecules.

At least six antibodies, namely, aducanumab, bapinerumab, crenezumab,gantenerumab, ponezumab, and solanezumab, specific for β-amyloid, whichis responsible for causing Alzheimer's disease, have been developed andplaced in clinical development. These antibodies generally fall short ofsatisfactory therapeutic efficacy in improving Alzheimer's disease. Ageneral belief is that if those antibodies are to achieve therapeuticefficacy, a significant portion must get across the BBB to enter theinjured sites in the CNS. However, only very minute portions of thoseantibodies get across the BBB.

Interferon-β-1a (IFN-β-1a) and interferon-β-1b (IFN-β-1b) have been usedfor the treatment of multiple sclerosis (MS). The pharmaceuticals,IFN-β-1a produced by mammalian cells and IFN-β-1b produced in E. coli,are one-chain protein of 166 amino acid residues containing onedisulfide bond. It has been claimed that those therapeutic agents reducerelapse of MS in 18-38% of treated patients. The mechanisms of action ofIFN-β-1a and IFN-β-1b are very complex and not completely understood,involving the increased generation of anti-inflammatory immune cells andfactors and the down-regulation of pro-inflammatory cells and factors.IFN-β treatment in MS patients also reduces the trafficking ofpro-inflammatory T cells across the BBB. It is yet unanswered whetherIFN-β-1a and IFN-β-1b mediate their pharmacologic effects in part bygetting into the injured sites in the CNS.

When an antibody or protein therapeutic is administered in the body'speripheral, only a very minute amount (about 0.1%) reaches to the CNS,because only a very minute portion of the protein therapeutic getsacross the BBB. However, it has also been found that in many diseases ofthe CNS, including Alzheimer's disease and multiple sclerosis, theinflammation at the diseased sites renders the BBB to breakdown, leadingto increased permeability. Therefore, we rationalize that if a largerproportion of an administered antibody specific for β-amyloid orIFN-β-1a and IFN-β-1b is channeled to the BBB, a higher percentage ofthe therapeutic agents can pass through the BBB and better therapeuticeffects can be achieved.

Furthermore, some therapeutic agents have been developed to inhibit theentry of inflammatory immunocytes to across the BBB. A notable exampleis natalizumab specific for the cell adhesion molecule integrin α4. Theantibody functions by inhibiting inflammatory immune cells to attach toand pass through the epithelial layer lining the BBB. While natalizumabhas been shown to be therapeutic efficacious, it has seriousimmunosuppressive side effect. In particular, it causes progressivemultifocal leukoencephalopathy, an opportunistic infection caused byJohn Cunningham virus (JC virus). We therefor rationalize that if alarger proportion of an antibody specific for integrin α4 is recruitedto the BBB, a smaller dose will be required, better therapeutic effectscan be achieved, and fewer side effects will occur.

The endothelial cells in the capillaries forming the BBB expresstransferrin receptors and insulin receptors, which mediate thetranscytosis of transferrin and insulin molecules, respectively, to thecerebral parenchyma. For using the transferrin receptor as a ferry, onlya small proportion gets through while the reaming bulk are trapped ordegraded. Because the endothelial cells lining the capillaries in otherparts of the vasculature do not express transferrin receptors, thetransferrin receptors on the endothelial cells in the BBB can serve assite-specific antigen for recruiting administered therapeutics. Once thetherapeutic is concentrated in the BBB, an increased proportion of itwill pass through the capillaries.

We also rationalize that when the mechanisms for channelingpharmaceuticals to the BBB is established, anti-inflammatory drugs, suchas anti-TNF-α, anti-IL12/IL-23, anti-IL17, and anti-CD3, should beinvestigated for their therapeutic effects on many types of diseases ofthe CNS.

For the antibody therapeutic specific for integrin α4, the transferrinreceptor is used as a target site recruiter. For Alzheimer disease, theeffector moiety can be a few copies of scFv specific for α-amyloid; fortreating multiple sclerosis, the effector moiety can be a few copies ofIFN-β-1a or IFN-β-1b, or a few copies of scFv specific for integrin α4.

Embodiments of the present disclosure disclose several T-E moleculesrespectively exist in single multi-arm linker-units or joint-linkerconfigurations, each contains scFv specific for transferrin receptor asthe targeting element and IFN-β-1a or IFN-β-1b or scFv specific forintegrin α-4 as the effector element. Alternative embodiments discloseT-E molecules respectively exist in single linker-units or joint-linkerconfigurations, each contains scFv specific for transferrin receptor asthe targeting element and scFv specific for β-amyloid as the effectorelement.

Fingolimod is an immunosuppressive drug that is derived from a naturalproduct myriocin originally isolated from certain fungi. Fingolimod hasbeen approved for reducing the relapse of relapsing-remitting multiplesclerosis. Fingolimod is phosphorylated in vivo to formfingolimod-phosphate, which resembles naturally occurringsphingosine-1-phosphate (S1P), an extracellular lipid mediator, and canbind to 4 of the 5 S1P receptors. The S1P receptors are expressed onlymphocytes and involved in lymphocyte migration. A generallypharmacologic mechanism of fingolimod is that it inhibits lymphocytesegress from the lymphoid tissues to the circulation and hence to theCNS. Fingolimod can cross BBB to enter CNS and many cell types in theCNS express S1P receptors, which play roles in cell proliferation,morphology, and migration. It is believed that fingolimod can havedirect on the CNS. The administration of fingolimod causes common sideeffects of headache and fatigue, and severe side effects of skin cancer,macular edema, and fatal infections, such as hemorrhaging focalencephalitis.

A fingolimod molecule has an NH2 group and thus provides a functionalgroup to couple with a bi-functional linker with an NHS group. Onepreferred embodiment of the present invention is to prepare a T-Econstruct, which contains a targeting element for delivery to the BBBand a drug bundle of fingolimod as an effector element. For a bundle offingolimod, 5-10 molecules are incorporated to a linker unit, usingeither a cleavable linker or non-cleavable linker to conjugatefingolimod molecules to the linking arms of a linker unit. Sincefingolimod, after uptake in a patient, is modified to fingolimodphosphate to resemble sphingosine1-phosphate and become active, the drugbundle is alternatively prepared with fingolimod phosphate. A linkerunit with fingolimod or fingolimod phosphate bundle is conjugated with 1or 2 scFv specific for a transferrin receptor I. Upon administration ofthe molecular construct, a portion of it is carried to the BBB. Thefingolimod molecules released from the cleavable linkers pass throughthe BBB and enter the CNS. Or, a portion of the entire construct entersthe CNS. Cleavable linkers can be designed by employing a number ofcleaving mechanisms. An installment of S—S bond is often used, since S—Sdisulfide bond can be cleaved by a reduction reaction at the targettissue site. A peptide bond between amino acids, which is sensitive toproteases, such as matrix metalloproteinases in many tissues andcathepsins in endosomes in target cells, is also commonly used as acleavable bond in many linker designs.

Some illustrative T-E molecules respectively exist in singlelinker-units or joint-linker configurations, each contains one or twoscFv specific for transferrin receptor as the targeting element andfingolimod as the effector element. In all these molecular constructs,the linkage between the linking arms and the effector elements may benon-cleavable or cleavable bonds. In applying the molecular constructplatforms of this invention for the various applications in treating CNSdiseases, the targeting moiety can be installed with one or two copiesof scFv specific for transferrin receptor or insulin receptor. One ortwo scFvs specific for transferrin receptor or insulin receptor areused. If the scFv has a relatively high affinity (Kd<1×10⁻⁹), 1 scFv isused; if the scFv has modest affinity (Kd<5×10⁻⁸ and >1×10⁻⁹), 2 scFvare used. It is preferred that no more than 2 copies of scFv specificfor transferrin receptor or insulin receptor are used to avoid receptorcross-linking and the endocytosis of the bound drug.

II Infectious Disease

Although large numbers of monoclonal antibodies have been made againstcomponents of a various viruses, bacteria, and fungi, which causeserious infectious in humans and animals, few monoclonal antibodies havebeen developed into preventive treatments or therapeutic agents tocounter infections. These shortcomings can be attributed to a few majorfactors. One major factor is the infectious microorganisms and theirproducts have different serotypes and variable reactivity toward aparticular antibody. Another reason is that the targeted microorganismsundergo mutations and escape the targeting of a particular antibody.

The T-E molecular design of the present invention can also be appliedfor the prevention and treatment of infectious diseases. The pluralityof the linking arms can enhance the avidity and specificity of bindingto target infectious microorganisms or their products and elicit immunefunctions to facilitate the clearance of the microorganisms and theirproducts. We reason that the avidity enhancement and the recruitment ofimmune clearance function can somehow overcome the serotypic differenceand mutational problems. Such improvements should increase the efficacyof the candidate antibodies for the prevention and therapy of infectiousdiseases. Many antibodies, which have failed to meet expectation inclinical trials, may be configured with the present invention andre-investigated.

A preferred set of embodiment of the present invention is to employjoint-linkers configuration with one linker-unit for targeting and onelinker-unit for recruiting effector function. An alternative set ofpreferred embodiment is to employ single linker-units with multiplelinking arms for targeting elements and a coupling arm for an effectorelement. The targeting elements may be one of the two categories: (1)scFv or sdAb specific for a surface component of a microorganism or itsproduct, e.g., envelope protein gp120 of human immunodeficiency virustype 1 (HIV-1), F protein of respiratory syncytia virus (RSV), a surfaceantigen of Clostridium difficile or Staphylococcus aureus, or endotoxinof Gram-negative bacteria or Shiga-like toxin of Escherichia coli, or(2) the extracellular portions of cell surface receptors of viruses,such as the HIV-1 gp120-binding CD4 domain.

The effector elements are 1 or 2 scFv or sdAb specific for one Fcreceptor of IgG, e.g. FcγRIIA (CD32), FcγRIIIB (CD16b), or FcγRI (CD64).Those receptors are expressed on neutrophils, macrophages, andeosinophils and are the key molecules mediating phagocytosis ofantibody-bound microorganisms. FcγRIIA and FcγRIIIB bind to IgG with lowaffinity (Kd in the range of 10⁻⁶ to 10⁻⁷), and FcγRI binds to IgG1 andIgG3 with high affinity (Kd 10⁻⁹). It is advantageous to employ scFv orsdAb specific for FcγRIIA or FcγRIIIB, because they can competefavorably with IgG in binding to the receptors.

The antibodies specific for carbohydrate antigens on bacterial surfaceare usually weak in binding affinity and are expressed in IgM ratherthan IgG. An IgM molecule has 10 Fv's (antigen-binding sites). However,an IgM molecule, which has a molecular weight of about 1000 kd, cannotcross capillaries and reach to extravascular space. With theconfiguration of the present invention, a molecular construct carrying 6scFv or 10 sdAb will have a molecular weight of about 150 kd.

In employing antibody-based therapeutics for clearing viruses, it isimportant that the therapeutic does not lead to FcR-mediated enhancementof viral infection. In those cases, the bound viral particles are notphagocytosed and digested. Some viruses, such as Dengue virus canmultiply in phagocytes. Thus, if the viral particles gain access to acell and enter the bound cells without being destroyed, the virus canmultiply in the infected cells. Therefore, a set of preferredembodiments of this invention is that the molecular construct contains 2or more scFv specific for an Fcγ receptor and can bind to multiple Fcγreceptor molecules on phagocyte cell surface, so that the bound viralparticles are destined to phagocytosis pathway.

Among the many antibodies specific for viruses, bacteria, or theirproducts, which have been in clinical trials, only antibodies specificfor RSV have been approved for clinical uses. Even for antibodiesagainst RSV, they are only approved for prevention, and not fortreatment of on-going infection. It is desirable that an anti-RSVantibody can be developed for treating already-infected subjects. Theother antibodies are still in clinical development or have failed inclinical trials. With the molecular construct platforms of thisinvention, all of these antibodies can be employed for improvedefficacy. A partial list of those antibodies are:

-   -   (1) Palivizumab and felvizumab specific for RSV F protein    -   (2) Suvizumab specific for HIV-1 gp120    -   (3) Libivirumab, exbivirumab, tuvirumab specific for hepatitis B        surface antigen (HBsAg) of HBV    -   (4) CR6261 mAb, diridavumab, and firivumab specific for        hemagglutinin A of influenza A virus    -   (5) Regavirumab and sevirumab specific for glycoprotein of        cytomegalovirus    -   (6) Rafivirumab specific for glycoprotein of rabies virus    -   (7) Actoxumab and bezlotoxumab specific for surface antigen of        Clostridium difficile    -   (8) Obiltoxaximab and raxibacumab specific for Bacillus        anthracis anthrax    -   (9) Panobacumab (human IgM monoclonal antibody) specific for        Pseudomonas aeruginosa serotype IATS O11    -   (10) Tefibazumab and tosatoxumab specific for clumping factor A        of Staphylococcus aureus    -   (11) Edobacomab specific for endotoxin of Gram-negative bacteria        for treating sepsis    -   (12) Pagibaximab specific for lipoteichoic acid of        staphylococcus areus for treating staphylococcal sepsis    -   (13) Raxibacumab (human monoclonal antibody) specific anthrax        toxin    -   (14) Pritoxaximab, setoxaximab, and urtoxazumab specific for        Shiga-like toxin type I or II of Escherichia coli.

According to several embodiments of the present disclosure, T-Emolecules in joint-linker configurations for treating infectiousdiseases incorporate scFv specific for the F protein of respiratorysyncytia virus (RSV) or gp120 of human immunodeficiency virus type 1(HIV-1) as targeting/capture elements and scFv specific for FcγRIIA(CD32) or FcγRIIIB (CD16b) as effector/clearance elements. According toembodiments of the present disclosure, some T-E molecules in singlelinker-units or joint linkers configuration incorporate scFv specificfor endotoxin of Gram(−) bacteria or lipoteichoic acid of Staphylococcusareus as targeting/capture elements and scFv specific for CD32 or CD16bas effector/clearance elements. An accelerated removal of endotoxinduring Gram(−) bacterial infection should decrease the amplitude ofcytokine release, such as TNF-α, IL-1 etc., (i.e. cytokine storm) in alife-threatening septic condition. In applying the molecular constructplatform of this invention for the various applications in treatinginfectious diseases, the effector moiety can be installed with one ortwo copies of scFv specific for transferrin receptor. One or two scFvsspecific for CD32 (CD32a or CD32b) or CD16b are used. If the scFv has arelatively high affinity (Kd<1×10⁻⁹), 1 scFv is used; if the scFv hasmodest affinity (Kd<5×10⁻⁸ and >1×10⁻⁹), 2 scFv are used. It ispreferred that no more than 2 copies of scFv specific for CD32 or CD16bare used to avoid receptor cross-linking and the endocytosis of thebound drug.

PART I Multi-Arm Linkers for Treating Specific Diseases

I-(i) Peptide Core for Use in Multi-Arm Linker

The first aspect of the present disclosure pertains to a linker unitthat comprises, (1) a center core that comprises 2-15 lysine (K)residues, and (2) 2-15 linking arms respectively linked to the Kresidues of the center core. The present center core is characterized inhaving or being linked with an azide group, an alkyne group, a tetrazinegroup, or a strained alkyne group at its N- or C-terminus.

In the preparation of the present linker unit, a PEG chain having aN-hydroxysuccinimidyl (NHS) group at one terminus and a functional group(e.g., an NHS, a maleimide, an azide, an alkyne, a tetrazine, or astrained alkyne group) at the other terminus is linked to the K residueof the center core by forming an amide bond between the NHS group of thePEG chain and the amine group of the K residue. In the presentdisclosure, the PEG chain linked to the K residue is referred to as alinking arm, which has a functional group at the free-terminus thereof.

According to the embodiments of the present disclosure, the center coreis a polypeptide that has 8-120 amino acid residues in length andcomprises 2 to 15 lysine (K) residues, in which each K residue and thenext K residue are separated by a filler sequence.

According to embodiments of the present disclosure, the filler sequencecomprises glycine (G) and serine (S) residues; preferably, the fillersequence consists of 2-15 residues selected from G, S, and a combinationthereof. For example, the filler sequence can be,

GS, GGS, GSG, GGGS, (SEQ ID NO: 1) GSGS, (SEQ ID NO: 2) GGSG,(SEQ ID NO: 3) GSGGS, (SEQ ID NO: 4) SGGSG, (SEQ ID NO: 5) GGGGS,(SEQ ID NO: 6) GGSGGS, (SEQ ID NO: 7) GGSGGSG, (SEQ ID NO: 8) SGSGGSGS,(SEQ ID NO: 9) GSGGSGSGS, (SEQ ID NO: 10) SGGSGGSGSG, (SEQ ID NO: 11)GGSGGSGGSGS, (SEQ ID NO: 12) SGGSGGSGSGGS, (SEQ ID NO: 13)GGGGSGGSGGGGS, (SEQ ID NO: 14) GGGSGSGSGSGGGS, (SEQ ID NO: 15) orSGSGGGGGSGGSGSG. (SEQ ID NO: 16)

The filler sequence placed between two lysine residues may be variationsof glycine and serine residues in somewhat random sequences and/orlengths. Longer fillers may be used for a polypeptide with fewer lysineresidues, and shorter fillers for a polypeptide with more lysineresidues. Hydrophilic amino acid residues, such as aspartic acid andhistidine, may be inserted into the filler sequences together withglycine and serine. As alternatives for filler sequences made up withglycine and serine residues, filler sequences may also be adopted fromflexible, soluble loops in common human serum proteins, such as albuminand immunoglobulins.

According to certain preferred embodiments of the present disclosure,the center core comprises 2-15 units of the sequence of G₁₋₅SK.Alternatively, the polypeptide comprises the sequence of (GSK)₂₋₁₅; thatis, the polypeptide comprises at least two consecutive units of thesequence of GSK. For example, the present center core may comprises theamino acid sequence of the following,

Ac-CGGSGGSGGSKGSGSK, (SEQ ID NO: 17) Ac-CGGSGGSGGSKGSGSKGSK,(SEQ ID NO: 18) or Ac-CGSKGSKGSKGSKGSKGSKGSKGSKGSKGSK, (SEQ ID NO: 19)in which Ac represents the acetyl group.

According to certain embodiments of the present disclosure, the centercore is a polypeptide that comprises the sequence of (X_(aa)—K)_(n), inwhich X_(aa) is a PEGylated amino acid having 2 to 12 repeats ofethylene glycol (EG) unit, and n is an integral from 2 to 15.

As described above, the present center core is characterized in havingor being linked with an azide group, an alkyne group, a tetrazine group,or a strained alkyne group at its N- or C-terminus. According to someembodiments of the present disclosure, the present center corecomprises, at its N- or C-terminus, an amino acid residue having anazide group or an alkyne group. The amino acid residue having an azidegroup can be, L-azidohomoalanine (AHA), 4-azido-L-phenylalanine,4-azido-D-phenylalanine, 3-azido-L-alanine, 3-azido-D-alanine,4-azido-L-homoalanine, 4-azido-D-homoalanine, 5-azido-L-ornithine,5-azido-d-ornithine, β-azido-L-lysine, or β-azido-D-lysine. For example,the present center core may have the sequence of,

Ac-(GSK)₂₋₇-(G₂₋₄S)₁₋₈-A^(AH),

Ac-A^(AH)-(SG₂₋₄)₁₋₈-(GSK)₂₋₇,

Ac-A^(AH)-(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈—C,

Ac—C—(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈-A^(AH),

Ac—K-(Xaa₂₋₁₂-K)₂₋₄-Xaa₂₋₁₂-A^(AH),

Ac-A^(AH)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₂₋₄,

Ac-A^(AH)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-C, or

Ac—C-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-A^(AH),

in which Xaa is a PEGylated amino acid having specified repeats of EGunit, Ac represents the acetyl group, and A^(AH) represents the AHAresidue.

Exemplary amino acid having an alkyne group includes, but is not limitedto, L-homopropargylglycine (L-HPG), D-homopropargylglycine (D-HPG), orbeta-homopropargylglycine (β-HPG). In this case, the present center coremay have the sequence of,

Ac-(GSK)₂₋₇-(G₂₋₄S)₁₋₈-G^(HP),

Ac-G^(HP)-(SG₂₋₄)₁₋₈-(GSK)₂₋₇,

Ac-G^(HP)-(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈—C,

Ac—C—(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈-G^(HP),

Ac—K-(Xaa₂₋₁₂-K)₂₋₄-Xaa₂₋₁₂-G^(HP),

Ac-G^(HP)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₂₋₄,

Ac-G^(HP)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-C, or

Ac—C-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-G^(HP),

in which Xaa is a PEGylated amino acid having specified repeats of EGunit, Ac represents the acetyl group, and G^(HP) represents the HPGresidue.

It is noted that many of the amino acids containing an azide or alkynegroup in their side chains and PEGylated amino acids are availablecommercially in t-boc (tert-butyloxycarbonyl)- or Fmoc(9-fluorenylmethyloxycarbonyl)-protected forms, which are readilyapplicable in solid-phase peptide synthesis.

According to some working examples of the present disclosure, the centercore may comprise the sequence of,

(SEQ ID NO: 21) Ac-G^(HP)GGSGGSGGSKGSGSK, (SEQ ID NO: 22)Ac-G^(HP)GGSGGSGGSKGSGSKGSK, (SEQ ID NO: 23)Ac-A^(AH)GGSGGSGGSKGSGSKGSK, (SEQ ID NO: 24)Ac-G^(HP)GGSGGSGGSKGSGSKGSGSC, (SEQ ID NO: 25)Ac-C-Xaa₂-K-Xaa₂-K-Xaa₂-K, or (SEQ ID NO: 26)Ac-C-Xaa₆-K-Xaa₆-K-Xaa₆-K-Xaa₆-K-Xaa₆-K,in which Xaa is a PEGylated amino acid having specified repeats of EGunit, Ac represents the acetyl group, A^(AH) represents the AHA residue,and G^(HP) represents the HPG residue.

Alternatively, the present center core is linked with a coupling arm,which has a functional group (e.g., an azide group, an alkyne group, atetrazine group, or a strained alkyne group) at the free-terminusthereof (that is, the terminus that is not linked to the center core).In these cases, the present center core comprises a cysteine residue atits N- or C-terminus. To prepare a linker unit linked with a couplingarm, a PEG chain having a maleimide group at one terminus and afunctional group at the other terminus is linked to the cysteine residueof the center core via thiol-maleimide reaction occurred between themaleimide group of the PEG chain and the thiol group of the cysteineresidue. In the present disclosure, the PEG chain linked to the cysteineresidue of the center core is referred to as the coupling arm, which hasa functional group at the free-terminus thereof.

Preferably, the coupling arm has a tetrazine group or a strained alkynegroup (e.g., a cyclooctene or cyclooctyne group) at the free-terminusthereof. These coupling arms have 2-12 EG units. According to theembodiments of the present disclosure, the tetrazine group is1,2,3,4-tetrazine, 1,2,3,5-tetrazine, 1,2,4,5-tetrazine, or derivativesthereof. The strained alkyne group may be a cyclooctene or a cyclooctynegroup. According to the working examples of the present disclosure, thecyclooctene group is a trans-cyclooctene (TCO) group; example ofcyclooctyne group includes, but is not limited to, dibenzocyclooctyne(DBCO), difluorinated cyclooctyne (DIFO), bicyclononyne (BCN), anddibenzocyclooctyne (DICO). According to some embodiments of the presentdisclosure, the tetrazine group is β-methyl-tetrazine.

Example of the present center core configured to be linked with thecoupling arm includes, but is not limited to,

Ac-(GSK)₂₋₇-(G₂₋₄S)₁₋₈—C-Xaa₂₋₁₂-tetrazine,

Ac-(GSK)₂₋₇-(G₂₋₄S)₁₋₈—C-Xaa₂₋₁₂-strained alkyne,

Ac—K-(Xaa₂₋₁₂-K)₂₋₄-Xaa₂₋₁₂-C-Xaa₂₋₁₂-tetrazine,

Ac—K-(Xaa₂₋₁₂-K)₂₋₄-Xaa₂₋₁₂-C-Xaa₂₋₁₂-strained alkyne,

Tetrazine-Xaa₂₋₁₂-C(Ac)—(SG₂₋₄)₁₋₈-(GSK)₂₋₇,

Strained alkyne-Xaa₂₋₁₂-C(Ac)—(SG₂₋₄)₁₋₈-(GSK)₂₋₇,

Tetrazine-Xaa₂₋₁₂-C(Ac)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₂₋₄, and

Strained alkyne-Xaa₂₋₁₂-C(Ac)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₂₋₄.

Alternatively, the center core has an azide or alkyne group at oneterminus and a coupling arm with tetrazine or strained alkyne group atthe other terminus. Examples are the following:

Ac-A^(AH)-(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈—C-Xaa₂₋₁₂-tetrazine,

Ac-A^(AH)-(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈—C-Xaa₂₋₁₂-strained alkyne,

Tetrazine-Xaa₂₋₁₂-C(Ac)—(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈-A^(AH),

Strained alkyne-Xaa₂₋₁₂-C(Ac)—(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈-A^(AH),

Ac-A^(AH)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-C-Xaa₂₋₁₂-tetrazine,

Ac-A^(AH)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-C-Xaa₂₋₁₂-strained alkyne,

Tetrazine-Xaa₂₋₁₂-C(Ac)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-A^(AH),

Strained alkyne-Xaa₂₋₁₂-C(Ac)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-A^(AH),

Ac-G^(HP)-(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈—C-Xaa₂₋₁₂-tetrazine,

Ac-G^(HP)-(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈—C-Xaa₂₋₁₂-strained alkyne,

Tetrazine-Xaa₂₋₁₂-C(Ac)—(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈-G^(HP),

Strained alkyne-Xaa₂₋₁₂-C(Ac)—(SG₂₋₄)₀₋₇-(GSK)₂₋₆-(G₂₋₄S)₁₋₈-G^(HP),

Ac-G^(HP)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-C-Xaa₂₋₁₂-tetrazine,

Ac-G^(HP)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-C-Xaa₂₋₁₂-strained alkyne,

Tetrazine-Xaa₂₋₁₂-C(Ac)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-G^(HP), and

Strained alkyne-Xaa₂₋₁₂-C(Ac)-Xaa₂₋₁₂-K-(Xaa₂₋₁₂-K)₁₋₃-Xaa₂₋₁₂-G^(HP).

The polypeptide may also be synthesized using recombinant technology byexpressing designed gene segments in bacterial or mammalian host cells.It is preferable to prepare the polypeptide as recombinant proteins ifthe core has high numbers of lysine residues with considerable lengths.As the length of a polypeptide increases, the number of errorsincreases, while the purity and/or the yield of the product decrease, ifsolid-phase synthesis was adopted. To produce a polypeptide in bacterialor mammalian host cells, a filler sequence ranges from a few amino acidresidues to 10-20 residues may be placed between two K residues.Further, since AHA and HPG are not natural amino acids encoded by thegenetic codes, the N-terminal or C-terminal residue for thoserecombinant polypeptides is cysteine. After the recombinant proteins areexpressed and purified, the terminal cysteine residue is then reactedwith short bifunctional cross-linkers, which have maleimide group at oneend, which reacts with SH group of cysteine residue, and alkyne, azide,tetrazine, or strained alkyne at the other end.

The synthesis of a polypeptide using PEGylated amino acids involvesfewer steps than that with regular amino acids such as glycine andserine resides. In addition, PEGylated amino acids with varying lengths(i.e., numbers of repeated ethylene glycol units) may be employed,offering flexibility for solubility and spacing between adjacent aminogroups of lysine residues. In addition to PEGylated amino acids, thecenter cores may also be constructed to comprise artificial amino acids,such as D-form amino acids, homo-amino acids, N-methyl amino acids, etc.Preferably, the PEGylated amino acids with varying lengths ofpolyethylene glycol (PEG) are used to construct the center core, becausethe PEG moieties contained in the amino acid molecules provideconformational flexibility and adequate spacing between conjugatinggroups, enhance aqueous solubility, and are generally weaklyimmunogenic. The synthesis of PEGylated amino acid-containing centercore is similar to the procedures for the synthesis of regularpolypeptides.

Optionally, for stability purpose, the present center core has an acetylgroup to block the amino group at its N-terminus.

As could be appreciated, the number of the linking arms linked to thecenter core is mainly determined by the number of lysine residescomprised in the center core. Since there are at least two lysineresidues comprised in the present center core, the present linker unitmay comprise a plurality of linking arms.

Reference is now made to FIG. 1A. As illustrated, the linker unit 10Acomprises a center core 11 a comprising one HPG (G^(HP)) residue andfour lysine (K) residues respectively separated by filler sequences(denoted by the dots throughout the drawings). The filler sequencesbetween the HPG residue and K residue or between any two K residues maycomprise the same or different amino acid sequences. In this example,four linking arms 20 a-20 d are linked to the lysine residues by formingan amide linkage between the NHS group and the amine group of the lysineresidue, respectively. As could be appreciated, certain featuresdiscussed above regarding the linker unit 10A or any other followinglinker units are common to other linker units disclosed herein, andhence some or all of these features are also applicable in the followingexamples, unless it is contradictory to the context of a specificembodiment. However, for the sake of brevity, these common features maynot be explicitly repeated below.

FIG. 1B provides a linker unit 10B according to another embodiment ofthe present disclosure. The center core 11 b comprises one cysteine (C)residue and six lysine (K) residues respectively separated by the fillersequences. In this example, the linker unit 10B comprises six linkingarms 20 a-20 f that are respectively linked to the lysine residues.According to the embodiments of the present disclosure, the linking armis a PEG chain having 2-20 repeats of EG units.

Unlike the linker unit 10A of FIG. 1A, the linker unit 1B furthercomprises a coupling arm 60. As discussed above, a PEG chain having amaleimide group at one end and a functional group at the other end isused to form the coupling arm 60. In this way, the coupling arm 60 islinked to the cysteine residue of the center core 11 b viathiol-maleimide reaction. In this example, the functional group at thefree terminus of the coupling arm 60 is a tetrazine group 72. Accordingto the embodiments of the present disclosure, the coupling arm is a PEGchain having 2-12 repeats of EG units.

When the release of effector elements at the targeted site is required,a cleavable bond can be installed in the linking arm. Such a bond iscleaved by acid/alkaline hydrolysis, reduction/oxidation, or enzymes.One embodiment of a class of cleavable PEG chains that can be used toform the coupling arm is NHS-PEG₂₋₂₀-S—S-maleimide, where S—S is adisulfide bond that can be slowly reduced, while the NHS group is usedfor conjugating with the amine group of the center core, thereby linkingthe PEG chain onto the center core. The maleimide group at the freeterminus of the linking arm may be substituted by an azide, alkyne,tetrazine, or strained alkyne group. According to some embodiments ofthe present disclosure, the linking arm is a PEG chain, which has 2-20repeats of EG units with a disulfide linkage at the free terminusthereof (i.e., the terminus that is not linked with the center core).Reference is now made to FIG. 1C, in which each of the five linking arms21 a-21 f respectively linked to the K resides of the center core 11 bis a PEG chain with a disulfide linkage at the free terminus of thelinking arm.

According to the embodiments of the present disclosure, the linking armlinked to the K residue of the center core has a functional group (i.e.,a maleimide, an NHS, an azide, an alkyne, a tetrazine, or a strainedalkyne group) at its free terminus. Preferably, when the free terminusof the linking arm is an azide, alkyne, or cyclooctyne group, then theamino acid residue at the N- or C-terminus of the center core is acysteine residue, and the free terminus of the coupling arm is atetrazine or cyclooctene group. Alternatively, when the free terminus ofthe linking arm is a tetrazine group or cyclooctene group, then theamino acid residue at the N- or C-terminus of the center core has anazide or alkyne group, or the amino acid residue at the N- or C-terminusof the center core is a cysteine residue, and the free terminus of thecoupling arm is an azide, the alkyne, or the cyclooctyne group

Depending on the functional group (i.e., a maleimide, an NHS, an azide,an alkyne, a tetrazine, or a strained alkyne group) present at the freeterminus of the linking arm, it is feasible to design a functionalelement (such as, a targeting element, an effector element, or anelement for improving the pharmacokinetic property) with a correspondingfunctional group, so that the functional element may linked to the freeterminus of the linking arm via any of the following chemical reactions,

(1) forming an amide bond therebetween: in this case, the linking armhas an NHS group at the free terminus, and the functional element has anamine group;

(2) the thiol-maleimide reaction: in this case, the linking arm has amaleimide group at the free terminus, and the functional element has anthiol group;

(3) the Copper(I)-catalyzed alkyne-azide cycloaddition reaction (CuAACreaction, or the “click” reaction for short): one of the free terminusof the linking arm and the functional element has an azide group, whilethe other has an alkyne group; the CuAAC reaction is exemplified inScheme 1;

(4) the inverse electron demand Diels-Alder (iEDDA) reaction: one of thefree terminus of the linking arm and the functional element has atetrazine group, while the other has a cyclooctene group; the iEDDAreaction is exemplified in Scheme 2; or

(5) the strained-promoted azide-alkyne click chemistry (SPAAC) reaction:one of the free terminus of the linking arm and the functional elementhas an azide group, while the other has an cyclooctyne group; the SPAACreaction is exemplified in Scheme 3.

The CuAAC reaction yields 1,5 di-substituted 1,2,3-triazole. Thereaction between alkyne and azide is very selective and there are noalkyne and azide groups in natural biomolecules. Furthermore, thereaction is quick and pH-insensitive. It has been suggested that insteadof using copper (I), such as cuprous bromide or cuprous iodide, forcatalyzing the click reaction, it is better to use a mixture of copper(II) and a reducing agent, such as sodium ascorbate to produce copper(I) in situ in the reaction mixture. Alternatively, the second elementcan be linked to the N- or C-terminus of the present center core via acopper-free reaction, in which pentamethylcyclopentadienyl rutheniumchloride complex is used as the catalyst to catalyze the azide-alkynecycloaddition.

For the sake of illustration, the functional elements linked to thelinking arms are referred to as the first elements. As could beappreciated, the number of the first elements carried by the presentlinker unit depends on the number of K residues of the center core (andthus, the number of the linking arms). Accordingly, one of ordinaryskill in the art may adjust the number of the first elements of thelinker unit as necessary, for example, to achieve the desired targetingor therapeutic effect.

An example of a linker unit 10D having the first elements is illustratedFIG. 1D. Other than the features discussed hereafter, FIG. 1D is quitesimilar to FIG. 1B. First, there are five K residues in the center core11 d, and accordingly, five linking arms 20 a-20 e are linked thereto,respectively. Second, the linker unit 10D has five first elements 30a-30 e linked to each of the linking arms 20 a-20 e. As discussed below,the optional tetrazine group 72 allows for the conjugation with anadditional functional element, another molecular construct (see, Part IIor Part III below).

FIG. 1E provides an alternative example, in which the linker unit 10Ehas a similar structure with the linker unit 1D, except that each of thelinker arms 21 a-21 e has a disulfide linkage at the element-linkingterminus thereof (i.e., the terminus that is linked with each of thefirst elements 30 a-30 e).

Alternatively, the present linker unit further comprises a pluralityconnecting arms, each of which has a functional group (i.e., amaleimide, an NHS, an azide, an alkyne, a tetrazine, or a strainedalkyne group) at one terminus, and an NHS or a maleimide group at theother terminus. Using a reaction that is similar to those occurredbetween the first element and the linking arm, the connecting arm may belinked to the linking arm with the corresponding functional group eithervia forming an amide bond therebetween, or via the thiol-maleimide,CuAAC, iEDDA or SPAAC reaction. The connecting arm linked to the linkingarm thus has the NHS or the maleimide group at its free terminus (or theelement-linking terminus; i.e., the terminus that is not linked with thelinking arm); then, the first element is linked to the element-linkingterminus of the connecting arm via forming an amide bond therebetween orvia the thiol-maleimide reaction.

Reference is now made to FIG. 1F, in which the linking arm is linked tothe K residue of the center core 11 d as described in FIG. 1D. Comparedwith the linker unit 10D, the linker unit 10F further comprises aconnecting arm 25, which is linked to the linking arms 22 via the SPAACreaction. Then, the first element 30 is linked to the connecting arm 25either via forming the amide bond therebetween or via thethiol-maleimide reaction. The diamond 90 as depicted in FIG. 1Frepresents the chemical bond resulted from the SPAAC reaction occurredbetween the linking arm 22 and the connecting arm 25.

According to some embodiments of the present disclosure, the connectingarm is a PEG chain having 2-20 repeats of EG units. Alternatively, theconnecting arm is a PEG chain having 2-20 repeats of EG units with adisulfide linkage at the element-linking terminus thereof (i.e., thefree terminus that is not linked with the linking arm).

In one working example, the connecting arm has three repeats of EGunits, as well as a disulfide linkage at the free terminus (alsoreferred to as the element-linking terminus) of the connecting arm. Inthis case, the first element linked to the element-linking terminus ofthe connecting arm can be efficiently released from the present linkerunit by the treatment of a reductant.

According to some preferred embodiments of the present disclosure, thefirst elements is fingolimod, fingolimod phosphate, interferon-β, or asingle-chain variable fragment (scFv) specific for integrin-α4,β-amyloid, a viral protein, a bacterial protein.

Non-limiting viral protein includes F protein of respiratory syncytiavirus (RSV), gp120 protein of human immunodeficiency virus type 1(HIV-1), hemagglutinin A (HA) protein of influenza A virus, andglycoprotein of cytomegalovirus.

Example of the bacterial protein includes, but is not limited to, theendotoxin of Gram(−) bacteria, the surface antigen of Clostridiumdifficile, the lipoteichoic acid of Saphylococcus aureus, the anthraxtoxin of Bacillus anthracis, or the Shiga-like toxin type I or II ofEscherichia coli.

In order to increase the intended or desired effect (e.g., thetherapeutic effect), the present linker unit may further comprise asecond element in addition to the first element. For example, the secondelement can be either a targeting element or an effector element. Inoptional embodiments of the present disclosure, the first element is aneffector element, while the second element may be another effectorelement, which works additively or synergistically with or independentlyof the first element. Still optionally, the first and second elementsexhibit different properties; for example, the first element is atargeting element, and the second element is an effector element, andvice versa. Alternatively, the first element is an effector element, andthe second element is an element capable of improving thepharmacokinetic property of the linker unit, such as solubility,clearance, half-life, and bioavailability. The choice of a particularfirst element and/or second element depends on the intended applicationin which the present linker unit (or multi-arm linker) is to be used.Examples of these functional elements are discussed below in PartI-(iii) of this specification.

Structurally, the second element is linked to the azide, alkyne,tetrazine, or strained alkyne group at the N- or C-terminus of thecenter core. Specifically, the second element may be optionallyconjugated with a short PEG chain (preferably having 2-12 repeats of EGunits) and then linked to the N- or C-terminal amino acid residue havingan azide group or an alkyne group (e.g., AHA residue or HPG residue).Alternatively, the second element may be optionally conjugated with theshort PEG chain and then linked to the coupling arm of the center core.

According to some embodiments of the present disclosure, the center corecomprises an amino acid having an azide group (e.g., the AHA residue) atits N- or C-terminus; and accordingly, a second element having an alkynegroup is linked to the N- or C-terminus of the center core via the CuAACreaction. According to other embodiments of the present disclosure, thecenter core comprises an amino acid having an alkyne group (e.g., theHPG residue) at its N- or C-terminus; and a second element having anazide group is thus capable of being linked to the N- or C-terminus ofthe center core via the CuAAC reaction.

FIG. 1G provides an example of the present linker unit 10G carrying aplurality of first elements and one second element. In this example, thecenter core 11 c comprises one HPG (G^(HP)) residue and five lysine (K)residues. Five linking arms 20 a-20 e are respectively linked to thefive K residues of the center core 11 c; and five first elements 30 a-30e are respectively linked to said five linking arms 20 a-20 e via thethiol-maleimide reaction. In addition to the first elements, the linkerunit 10G further comprises one second element 50 that is linked to oneend of a short PEG chain 62. Before being conjugated with the centercore 11 c, the other end of the short PEG chain 62 has an azide group.In this way, the azide group may reacted with the HPG residue thathaving an alkyne group via CuAAC reaction, so that the second element 50is linked to the center core 11 c. The solid dot 40 depicted in FIG. 1Grepresents the chemical bond resulted from the CuAAC reaction occurredbetween the HPG residue and the azide group.

Alternatively, the second element is linked to the center core via acoupling arm. According to certain embodiments of the presentdisclosure, the coupling arm has a tetrazine group, which can beefficiently linked to a second element having a TCO group via the iEDDAreaction. According to other embodiments of the present disclosure, thecoupling arm has a TCO group, which is capable of being linked to asecond element having a tetrazine group via the iEDDA reaction. In theiEDDA reaction, the strained cyclooctenes that possess a remarkablydecreased activation energy in contrast to terminal alkynes is employed,and thus eliminate the need of an exogenous catalyst.

Reference is now made to FIG. 1H, in which the center core 11 d of thelinker unit 10H comprises a terminal cysteine (C) residue and fivelysine (K) residues. As depicted in FIG. 1H, five linking arms 20 a-20 eare respectively linked to the five K residue of the center core 11 d,and then five first elements 30 a-30 e are respectively linked to thefive linking arms 20 a-20 e via thiol-maleimide reactions. The cysteineresidue is linked to the coupling arm 60, which, before being conjugatedwith the second element, comprises a tetrazine group or a TCO group atits free-terminus. In this example, a second element 50 linked with ashort PEG chain 62 having a corresponding TCO or tetrazine group can belinked to the coupling arm 60 via the iEDDA reaction. The ellipse 70 asdepicted in FIG. 1H represents the chemical bond resulted from the iEDDAreaction occurred between the coupling arm 60 and the short PEG chain62.

According to other embodiments of the present disclosure, before theconjugation with a second element, the coupling arm has an azide group.As such, the coupling arm can be linked to the second element having acyclooctyne group (e.g., the DBCO, DIFO, BCN, or DICO group) at thefree-terminus of a short PEG chain via SPAAC reaction, and vice versa.

Reference is now made to FIG. 11, in which the linker unit 10I has astructure similar to the linker unit 10H of FIG. 1H, except that thecoupling arm 60 comprises an azide or a cyclooctyne group (e.g., theDBCO, DIFO, BCN, or DICO group), instead of the tetrazine or TCO group.Accordingly, the second element 50 linked with a short PEG chain 62 mayhave a corresponding cyclooctyne (e.g., DBCO, DIFO, BCN, or DICO) orazide group, so that it can be linked to the coupling arm 60 via theSPAAC reaction. The diamond 90 as depicted in FIG. 11 represents thechemical bond resulted from the SPAAC reaction occurred between thecoupling arm 60 and the short PEG chain 62.

Scheme 4 is an exemplary illustration of the process of preparing thepresent linker unit. In step 1, the center core comprising the aminoacid sequence of (GSK)₃ and a L-azidohomoalanine (AHA) residue at theC-terminus thereof is prepared. In step 2, three linking arms arerespectively linked to the lysine (K) residues of the center core viaforming an amide bond between the NHS group and the amine group; thelinking arm linked to the center core has a maleimide (Mal) group at thefree-terminus thereof. In step 3, three anti-A antigen scFvs (scFv α A)as the first element are respectively linked to the linking arms via thethiol-maleimide reaction. Meanwhile, in step 4, one anti-B antigen scFv(scFv α B) as the second element is linked with a short PEG chain thathas 4 repeats of EG units and a DBCO group at the free terminus.Finally, in step 5, the second element is linked to the AHA residue ofthe center core via the SPAAC reaction.

Scheme 5 illustrates another example of the process for preparing thepresent linker unit. In step 1, the center core comprising the aminoacid sequence of (K-Xaa)₃ and a cysteine residue at the C-terminusthereof is prepared. In step 2, a PEG chain (as the coupling arm) thathas the maleimide (Mal) group at one terminus and a tetrazine group atthe other terminus is linked to the cysteine residue via thethiol-maleimide reaction. Then, in step 3, three linking arm arerespectively linked to the lysine (K) residues of the center core. Next,three anti-A antigen scFvs (scFv α A) as the first elements arerespectively linked to the linking arms via the thiol-maleimide reactionas described in step 4. Meanwhile, in step 5, one anti-B antigen scFv(scFv α B) as the second element is linked with a short PEG chain thathas 3 repeats of EG units and a TCO group at the free terminus. Finally,in step 6, the second element is linked to the coupling arm via theiEDDA reaction.

PEGylation is a process, in which a PEG chain is attached or linked to amolecule (e.g., a drug or a protein). It is known that PEGylationimparts several significant pharmacological advantages over theunmodified form, such as improved solubility, increased stability,extended circulating life, and decreased proteolytic degradation.According to one embodiment of the present disclosure, the secondelement is a PEG chain, which has a molecular weight of about 20,000 to50,000 daltons.

FIG. 1J provides an alternative example of the present linker unit(linker unit 10J), in which five first elements 30 are respectivelylinked to the lysine residues via the linking arms 20, and the AHA(A^(AH)) residue of the center core Ile is linked with a PEG chain 80via the CuAAC reaction. The solid dot 40 depicted in FIG. 1J representsthe chemical bond resulted from the CuAAC reaction occurred between theAHA residue and the PEG chain 80.

FIG. 1K provides another example of the present disclosure, in which theN-terminus of the center core 11 d is a cysteine residue that is linkedto a coupling arm 60. A PEG chain 80 can be efficiently linked to thecoupling arm 60 via the iEDDA reaction. The ellipse 70 of the linkerunit 10K represents the chemical bond resulted from the iEDDA reactionoccurred between the coupling arm 60 and the PEG chain 80.

FIG. 1L provides an alternative example of the present linker unit, inwhich the linker unit 10L has a structure similar to the linker unit 10Jof FIG. 1J, except that the PEG chain 80 is linked to the coupling arm60 via the SPAAC reaction. The diamond 90 depicted in FIG. 1K representsthe chemical bond resulted from the SPAAC reaction occurred between thecoupling arm 60 and the PEG chain 80.

According to some embodiments of the present disclosure, in addition tothe first and second elements, the present linker unit further comprisesa third element. In this case, one of the N- and C-terminus of thecenter core is an amino acid having an azide group or an alkyne group,while the other of the N- and C-terminus of the center core is acysteine residue. The lysine residues of the center core arerespectively linked with the linking arms, each of which has a maleimidegroup at its free terminus; whereas the cysteine residue of the centercore is linked with the coupling arm, which has a tetrazine group or astrained alkyne group at its free terminus. As described above, thefirst element is therefore linked to the linking arm via thethiol-maleimide reaction, and the second element is linked to thecoupling arm via the iEDDA reaction. Further, a third element is linkedto the terminal amino acid having an azide group or an alkyne group viathe CuAAC reaction or SPAAC reaction.

Reference is now made to the linker unit 10M of FIG. 1M, in which thecenter core 11 f has an HPG (G^(HP)) residue at the N-terminus thereofand a cysteine residue at the C-terminus thereof. The linking arms 20and the coupling arm 60 are respectively linked to the lysine (K)residues and the cysteine (C) residue of the center core 11 f. Further,five first elements 30 are respectively linked to the five linking arms20, the second element (i.e., the PEG chain) 80 is linked to thecoupling arm 60 via the short PEG chain 62, and the third element 50 islinked to the HPG residue. The solid dot 40 indicated the chemical bondresulted from the CuAAC reaction occurred between the HPG residue andthe short PEG chain 62; while the ellipse 70 represents the chemicalbond resulted from the iEDDA reaction occurred between the coupling arm60 and the PEG chain 80.

FIG. 1N provides another embodiment of the present disclosure, in whichthe linker unit 10N has the similar structure with the linker unit 10Mof FIG. 1M, except that the short PEG chain 62 is linked with the HPGresidue via the SPAAC reaction, instead of the iEDDA reaction. Thediamond 90 in FIG. 1N represents the chemical bond resulted from theSPAAC reaction occurred between the short PEG chain 62 and the HPGresidue.

In the preferred embodiments of this disclosure, the linking arms have amaleimide group in the free terminus for conjugating with first elementshaving the sulfhydryl group via the thiol-maleimide reaction. Also,there is one cysteine residue or an amino acid residue with an azide oralkyne group at a terminus of the peptide core for attaching a couplingarm for linking a second element.

It is conceivable for those skilled in the arts that variations may bemade. A conjugating group, other than maleimide, such as azide, alkyne,tetrazine, or strained alkyne may be used for the free terminus of thelinking arms, for linking with first elements with a CuAAC, iEDDA, orSPAAC reaction. Also the cysteine residue (or an amino acid residue withan azide or alkyne group) of the peptide core needs not to be at the N-or C-terminus. Furthermore, two or more of such residues may beincorporated in the peptide core to attach multiple coupling arms forlinking a plural of second elements.

I-(ii) Compound Core for Use in Multi-Arm Linker

In addition to the linker unit described in part I-(i) of the presentdisclosure, also disclosed herein is another linker unit that employs acompound, instead of the polypeptide, as the center core. Specifically,the compound is benzene-1,3,5-triamine,2-(aminomethyl)-2-methylpropane-1,3-diamine, tris(2-aminoethyl)amine,benzene-1,2,4,5-tetraamine, 3,3″,5,5′-tetraamine-1,1-biphenyl,tetrakis(2-aminoethyl)methane, tetrakis-(ethylamine)hydrazine,N,N,N′,N″,-tetrakis(aminoethyl)ethylenediamine,benzene-1,2,3,4,5,6-hexaamine,1-N,1-N,3-N,3-N,5-N,5-N-hexakis(methylamine)-benzene-1,3,5-triamine,1-N,1-N,2-N,2-N,4-N,4-N,5-N,5-N,-octakis(methylamine)-benzene-1,2,4,5-triamine,benzene-1,2,3,4,5,6-hexaamine, orN,N-bis[(1-amino-3,3-diaminoethyl)pentyl]-methanediamine. Each of thesecompounds has 3 or more amine groups in identical or symmetricalconfiguration. Therefore, when one of the amine groups of a compound isconjugated with a coupling arm, all of the molecules of the compoundhave the same configuration.

Similar to the mechanism of linkage described in Part I-(i) of thepresent disclosure, each compound listed above comprises a plurality ofamine groups, and thus, a plurality of PEG chains having NHS groups canbe linked to the compound via forming an amine linkage between the aminegroup and the NHS group; the thus-linked PEG chain is designated aslinking arm, which has a functional group (e.g., an NHS, a maleimide, anazide, an alkyne, a tetrazine, a cyclooctene, or a cyclooctynep group)at the free-terminus thereof. Meanwhile, at least one of the aminegroups of the compound core is linked to another PEG chain, which has anNHS group at one end, and a functional group (e.g., an azide, alkyne,tetrazine, a cyclooctene, or a cyclooctynep group) at the other end; thethus-linked PEG chain is designated as coupling arm, which has afunctional group at the free-terminus thereof.

Accordingly, a first element can be linked to the linking arm via (1)forming an amide bond therebetween, (2) the thiol-maleimide reaction,(3) the CuAAC reaction, (4) the iEDDA reaction, or (5) SPAAC reaction.Meanwhile, the second element can be linked to the coupling arm via theCuAAC, iEDDA or SPAAC reaction. t.

According to some embodiments of the present disclosure, the linking armis a PEG chain having 2-20 repeats of EG units; preferably, the linkingarm is a PEG chain having 2-20 repeats of EG units with a disulfidelinkage at the free terminus thereof (i.e., the terminus that is notwith the center core). The coupling arm is a PEG chain having 2-12repeats of EG unit. In one embodiment, both the linking and couplingarms have 12 repeats of EG unit, in which one terminus of the couplingarm is an NHS group, and the other terminus of the coupling arm is analkyne group.

According to an alternative embodiment of the present disclosure, thelinker unit further comprises a plurality of connecting arms, each ofwhich is linked to each of the linking arm. Then, a plurality of thefirst elements are respectively linked to the plurality of connectingarms. In one embodiment, the connecting arm is a PEG chain having 2-20repeats of EG units. In another embodiment, the connecting arm is a PEGchain having 2-20 repeats of EG units with a disulfide linkage at theelement-linking terminus that is not linked with the linking arm.

Schemes 6 and 7 respectively depict the linkages between the centercompound core and the linking arm, as well as the coupling arm. Inschemes 6 and 7, “NHS” represents the NHS ester, “Mal” represents themaleimide group, “azide” represents the azide group, and “alkyne”represents the alkyne group.

The requirement of having multiple NH₂ groups exist in a symmetrical andidentical orientation in the compound serving as the center core is forthe following reason: when one of the NH₂ group is used for connecting abifunctional linker arm with N-hydroxysuccinimidyl (NHS) ester group andalkyne, azide, tetrazine, or strained alkyne group, the product, namely,a core with a coupling arm having alkyne, azide, tetrazine or strainedalkyne, is homogeneous and may be purified. Such a product can then beused to produce multi-arm linker units with all other NH₂ groupsconnected to linking arms with maleimide or other coupling groups at theother ends. If a compound with multiple NH₂ groups in non-symmetricalorientations, the product with one bifunctional linking arm/couplingarms is not homogeneous.

Some of those symmetrical compounds can further be modified to providecenter cores with more linking arms/coupling arms. For example,tetrakis(2-aminoethyl)methane, which can be synthesized from commoncompounds or obtained commercially, may be used as a core forconstructing linker units with four linking arms/coupling arms.Tetrakis(2-aminoethyl)methane can react withbis(sulfosuccinimidyl)suberate to yield a condensed product of twotetrakis(2-aminoethyl)methane molecules, which can be used as a core forconstructing linker units having six linking arms/coupling arms. Thelinker units, respectively having 3 linking arms/coupling arms, 4linking arms/coupling arms and 6 linking arms/coupling arms, can fulfillmost of the need for constructing targeting/effector molecules withjoint-linker configuration.

As would be appreciated, the numbers of the linking arm and/or thecoupling arm and the element linked thereto may vary with the number ofamine groups comprised in the center core. In some preferredembodiments, the numbers of the linking arm/coupling arm and thecorresponding linking element linked thereto ranges from about 1-7.

Reference is now made to FIG. 2, in which benzene-1,2,4,5-tetraaminehaving 4 amine groups is depicted. Three of the amine groups arerespectively linked to the linking arms 20, and one of the amine groupis linked to the coupling arm 60, which has an azide group at itsfree-terminus. Three first elements 30 are then respectively linked tothe three linking arms 20 via the thiol-maleimide reactions, and onesecond element 50 is linked to the coupling arm 60 via the CuAACreaction. The solid dot 40 as depicted in FIG. 2 represents the chemicalbond resulted from the CuAAC reaction occurred between the coupling arm60 and the second element 50.

I-(iii) Functional Elements Suitable for Use in Multi-Arm Linker

In the case where the linker unit (or multi-arm linker) comprises onlythe first element but not the second and/or third element(s), the firstelement is an effector element that may elicit a therapeutic effect in asubject. On the other hand, when the present linker unit compriseselements in addition to first element(s), then at least one of theelements is an effector element, while the other may be another effectorelement, a targeting element, or an element capable of enhancing one ormore pharmacokinetic properties of the linker unit (e.g., solubility,clearance, half-life, and bioavailability). For example, the linker unitmay have two different kinds of effector element, one effector elementand one targeting element or one pharmacokinetic property-enhancingelement, two different kinds of targeting elements and one kind ofeffector element, two different kinds of effector elements and one kindof targeting element, or one kind of targeting element, one kind ofeffector element and one element capable of improving thepharmacokinetic property of the linker unit.

According to certain embodiments of the present disclosure, thetargeting element or the effector element is fingolimod, fingolimodphosphate, interferon-β, or a single-chain variable fragment (scFv)specific for integrin-α4, β-amyloid, a viral protein, or a bacterialprotein.

Examples of viral proteins include, but are not limited to, F protein ofrespiratory syncytia virus (RSV), gp120 protein of humanimmunodeficiency virus type 1 (HIV-1), hemagglutinin A (HA) protein ofinfluenza A virus, and glycoprotein of cytomegalovirus.

Illustrative examples of bacterial protein include endotoxin of Gram(−)bacteria, surface antigen of Clostridium difficile, lipoteichoic acid ofSaphylococcus aureus, anthrax toxin of Bacillus anthracis, andShiga-like toxin type I or II of Escherichia coli.

Elements that enhance one or more pharmacokinetic properties of thelinker unit can be a long PEG chain having a molecular weight of about20,000 to 50,000 daltons.

Specific examples of the functional elements incorporated in the presentmulti-arm linker for treating a particular disease are discussed below.

To treat a CNS disease, such as multiple sclerosis, one exemplary linkerunit may use fingolimod, fingolimod phosphate, interferon-β, or an scFvspecific for integrin-α4 as the first element (effector element). Totreat Alzheimer's disease, the present linker unit may use an scFvspecific for 3-amyloid as the first element (effector element).Optionally, the linker unit for treating multiple sclerosis, Alzheimer'sdisease, or other CNS diseases may further comprise a second element ofan scFv specific for transferrin receptor as the targeting element.

Similarly, an scFv specific for a viral or bacterial protein can be usedas the targeting element (first element) in order to treat the infectioncaused by the virus or bacterium. In these cases, the linker unit maycomprise an optional second element, such as an scFv specific for CD32or CD16b, as the effector element.

I-(iv) Use of Multi-Arm Linker

The present disclosure also pertains to method for treating variousdiseases using the suitable linker unit. Generally, the method comprisesthe step of administering to a subject in need of such treatment aneffective amount of the linker unit according to embodiments of thepresent disclosure.

Compared with previously known therapeutic constructs, the presentlinker unit discussed in Part I is advantageous in two points:

(1) The number of the functional elements may be adjusted in accordancewith the needs and/or applications. The present linker unit may comprisetwo elements (i.e., the first and second elements) or three elements(i.e., the first, second, and third elements) in accordance with therequirements of the application (e.g., the disease being treated, theroute of administration of the present linker unit, and the bindingavidity and/or affinity of the antibody carried by the present linkerunit). For example, when the present linker unit is directly deliveredinto the tissue/organ (e.g., the treatment of eye), one element actingas the effector element may be enough, thus would eliminate the need ofa second element acting as the targeting element. However, when thepresent linker unit is delivered peripherally (e.g., oral, enteral,nasal, topical, transmucosal, intramuscular, intravenous, orintraperitoneal injection), it may be necessary for the present linkerunit to simultaneously comprise a targeting element that specificallytargets the present linker unit to the lesion site; and an effectorelement that exhibits a therapeutic effect on the lesion site. For thepurpose of increasing the targeting or treatment efficacy or increasingthe stability of the present linker unit, a third element (e.g., asecond targeting element, a second effector element, or a PEG chain) maybe further included in the present linker unit.

(2) The first element is provided in the form of a bundle. As describedabove, the number of the first element may vary with the number oflysine residue comprised in the center core. If the number of lysineresidue in the center core ranges from 2 to 15, then at least two firstelements may be comprised in each linker unit. Thus, instead ofproviding one single molecule (e.g., cytotoxic drug and antibody) astraditional therapeutic construct or method may render, the presentlinker unit is capable of providing more functional elements (either astargeting elements or as effector elements) at one time, thereby greatlyimproves the therapeutic effect.

In certain therapeutic applications, it is desirable to have a singlecopy of a targeting or effector element. For example, a single copy of atargeting element can be used to avoid unwanted effects due to overlytight binding. This consideration is relevant, when the scFv has arelatively high affinity for the targeted antigen and when the targetedantigen is a cell surface antigen on normal cells, which are nottargeted diseased cells. As an example, in using scFv specific for CD3or CD16a to recruit T cells or NK cells to kill targeted cells, such asthyroid gland cells in patients with Graves' disease, a single copy ofthe scFv specific for CD3 or CD16a is desirable, so that unwantedeffects due to cross-linking of the CD3 or CD16a may be avoided.Similarly, in using scFv specific for CD32 or CD16b to recruitphagocytic neutrophils and macrophages to clear antibody-bound viral orbacterial particles or their products, a single copy of scFv may bedesirable. Also, in using scFv specific for transferrin receptor tocarry effector drug molecules to the BBB for treating CNS diseases, asingle copy of scFv specific for transferrin receptor is desirable. Instill another example, it is desirable to have only one copy oflong-chain PEG for enhancing pharmacokinetic properties. Two or morelong PEG chains may cause tangling and affect the binding properties ofthe targeting or effector elements.

EXPERIMENTAL EXAMPLES Example 1 Synthesis of Peptide 1 (SEQ ID NO: 18),Peptide 2 (SEQ ID NO: 27) and Peptide 3 (SEQ ID NO: 19) as PeptideCores, and Conjugation of the SH Group of their Cysteine Residue withMaleimide-PEG₃-Transcyclooctene (TCO) as a Coupling Arm

The synthesized peptides 1, 2 and 3 (Chinapeptide Inc., Shanghai, China)were processed similarly. Each peptide was dissolved in 100 mM sodiumphosphate buffer (pH 7.0) containing 50 mM NaCl and 5 mM EDTA at a finalconcentration of 2 mM. The dissolved peptide was reduced by 1 mMtris(2-carboxyethyl)phosphine (TCEP) at 25° C. for 2 hours. Forconjugating the SH group of the cysteine residue with maleimide-PEG₃-TCO(Conju-probe Inc.) to create a functional linking group TCO, the peptideand maleimide-PEG₃-TCO were mixed at a 1/7.5 molar ratio and incubatedat pH 7 and 25° C. for 18 hours. The TCO-conjugated peptide was purifiedby reverse phase HPLC on a Supelco C18 column (250 mm×10 mm; 5 μm),using a mobile phase of acetonitrile and 0.1% trifluoroacetic acid, alinear gradient of 0% to 100% acetonitrile over 30 minutes, at a flowrate of 1.0 mL/min and a column temperature of 25° C.

The identification of the synthesized TCO-peptides (illustrated below)was carried out by MALDI-TOF mass spectrometry. Mass spectrometryanalyses were performed by the Mass Core Facility at the Institute ofMolecular Biology (IMB), Academia Sinica, Taipei, Taiwan. Measurementswere performed on a Bruker Autoflex III MALDI-TOF/TOF mass spectrometer(Bruker Daltonics, Bremen, Germany).

The synthesized TCO-peptide 1, as illustrated below, had a molecularweight (m.w.) of 2,078.9 daltons.

The synthesized TCO-peptide 2, as illustrated below, had a m.w. of2,020.09 daltons.

The TCO-peptide 3, as illustrated below, had a m.w. of 3,381.85 daltons.

Example 2 Synthesis of Peptide 1 as a Peptide Core, and Conjugation ofthe SH Group of its Cysteine Residue with Maleimide-PEG₄-Tetrazine as aCoupling Arm

The synthesized peptide 1 (Chinapeptide Inc., Shanghai, China) wasdissolved in 100 mM sodium phosphate buffer (pH 7.0) containing 50 mMNaCl and 5 mM EDTA at a final concentration of 2 mM. The dissolvedpeptide was reduced by 1 mM tris(2-carboxyethyl)phosphine (TCEP) at 25°C. for 2 hours. For conjugating the SH group of the cysteine residuewith maleimide-PEG₄-tetrazine (Conju-probe Inc., San Diego, USA) tocreate a functional linking group tetrazine, the peptide andmaleimide-PEG₄-tetrazine were mixed at a 1/5 ratio and incubated at pH 7and 4° C. for 18 hours. The tetrazine-conjugated peptide was purified byreverse phase HPLC on a Supelco C18 column (250 mm×10 mm; 5 μm), using amobile phase of acetonitrile and 0.1% trifluoroacetic acid, a lineargradient of 0% to 100% acetonitrile over 30 minutes, at a flow rate of1.0 mL/min and a column temperature of 25° C.

The synthesized tetrazine-peptide 1, as illustrated below, had a m.w. of2,185.2 daltons.

Example 3 Synthesis of a Linker Unit by Conjugating NHS-PEG₁₂-Mal to NH₂Groups of TCO-Peptide 1 as Linking Arms

Three linking arms of PEG₁₂-maleimide were attached to the peptide core,

TCO-peptide 1. The crosslinker, NHS-PEG₁₂-maleimide(succinimidyl-[(N-maleimido-propionamido)-dodecaethyleneglycol] ester,was purchased from Thermo Fisher Scientific Inc. (Waltham, USA). Theconjugation procedure was performed per the manufacturer's instruction.Briefly, the peptide with lysine residues was dissolved in theconjugation buffer, phosphate buffered saline (pH 7.5) at 100 mM.NHS-PEG₁₂-maleimide crosslinker was then added to the dissolved peptideat a 1 mM final concentration (10-fold molar excess over 0.1 mM peptidesolution). The reaction mixtures were incubated for 18 hours at roomtemperature. The maleimide-PEG₁₂-conjugated TCO-peptide 1 was purifiedby reverse phase HPLC on a Supelco C18 column (250 mm×4.6 mm; 5 μm),using a mobile phase of acetonitrile and 0.1% trifluoroacetic acid, alinear gradient of 0% to 100% acetonitrile over 30 minutes, at a flowrate of 1.0 mL/min and a column temperature of 25° C.

The identification of the maleimide-PEG₁₂-conjugated TCO-peptide 1 wascarried out by mass spectrometry MALDI-TOF.

The synthesized maleimide-PEG₁₂-conjugated TCO-peptide1 had a m.w. of4,332 daltons. As illustrated below, the maleimide-PEG₁₂-conjugatedTCO-peptide1 is a peptide-core based linker unit carrying one TCO groupand three PEG linking arms with maleimide groups.

Example 4 Synthesis of a Linker Unit by Conjugating NHS-PEG₁₂-Mal to NH₂Groups of Tetrazine-Peptide 1 as Linking Arms

Three linking arms of PEG₁₂-maleimide were attached to the peptide core,tetrazine-peptide 1. The crosslinker, NHS-PEG₁₂-maleimide(succinimidyl-[(N-maleimido-propionamido)-dodecaethyleneglycol] ester,was purchased from Thermo Fisher Scientific Inc. (Waltham, USA). Theconjugation procedure was performed per the manufacturer's instruction.Briefly, the peptide with lysine residues was dissolved in theconjugation buffer, phosphate buffered saline (pH 7.5) at 100 mM.NHS-PEG₁₂-maleimide crosslinker was then added to the dissolved peptideat a 1 mM final concentration (10-fold molar excess over 0.1 mM peptidesolution). The reaction mixtures were incubated for 18 hours at roomtemperature. The maleimide-PEG₁₂-conjugated tetrazine-peptide 1 waspurified by reverse phase HPLC on a Supelco C18 column (250 mm×4.6 mm; 5μm), using a mobile phase of acetonitrile and 0.1% trifluoroacetic acid,a linear gradient of 0% to 100% acetonitrile over 30 minutes, at a flowrate of 1.0 mL/min and a column temperature of 25° C.

The synthesized maleimide-PEG₁₂-conjugated tetrazine-peptide1, asillustrated herein, was a peptide-core based linker unit carrying onetetrazine group and three PEG linking arms with maleimide groups. FIG. 2shows the MALDI-TOF result, indicating that the construct had a m.w. of4,461 daltons.

Example 5 Conjugation of Fingolimod and Fingolimod Phosphate Moleculewith an NHS-PEG₅-NHS Cross-Linker

Fingolimod was purchased from Biotang Inc. (Lexington, USA) andfingolimod phosphate from KM3 Scientific Corporation (New Taipei City,Taiwan). The NH₂ group of fingolimod molecule was reacted with ahomo-bifunctional crosslinker, NHS-PEG₅-NHS, as shown in scheme 8.Fingolimod was dissolved in 100% DMSO at a final concentration of 10 mM;NHS-PEG₅-NHS was dissolved in 100% DMSO at a 250 mM final concentration.To activate the NH₂ group of fingolimod, 6% (v/v) of basic sodiumphosphate buffer (pH12.7) was added to the fingolimod solution and thenincubated for 10 minutes. NHS-PEG₅-NHS crosslinker was added to thedissolved fingolimod solution at a final concentration of 30 mM (3-foldmolar excess over 10 mM fingolimod solution). The reaction mixture wasincubated for 3 hours at room temperature.

Fingolimod phosphate was dissolved in 100% DMSO at a final concentrationof 5 mM, and NHS-PEG₅-NHS crosslinker was dissolved in 100% DMSO at afinal concentration of 250 mM. NHS-PEG₅-NHS crosslinker was added to thedissolved fingolimod phosphate solution at a 15 mM final concentration(3-fold molar excess over 5 mM fingolimod phosphate solution). Thereaction mixture was incubated for 3 hours at room temperature, then 18%(v/v) acid sodium phosphate buffer (pH=0.88) was added to quench thereaction. The solvent was evaporated under vacuum.

NHS-PEG₅-conjugated fingolimod and NHS-PEG₅-conjugated fingolimodphosphate were dissolved in 30% acetonitrile, and then purified usingreverse phase HPLC on a Supelco C18 column (250 mm×4.6 mm; 5 μm), usinga mobile phase of acetonitrile and 0.1% trifluoroacetic acid, a lineargradient of 30% to 100% acetonitrile over 30 minutes, at a flow rate of1.0 mL/min and a column temperature of 25° C.

FIG. 3 shows that the synthesized NHS-PEG₅-conjugated fingolimod, asillustrated in scheme 8, had a m.w. of 725.41 daltons.

The synthesized NHS-PEG₅-conjugated fingolimod phosphate, as illustratedbelow, had a m.w. of 803.3 daltons.

Example 6 Conjugation of Fingolimod Molecule with an NHS—S—S—PEG₃-AzidoLinking Arm

The NH₂ group of fingolimod molecule was reacted with ahetero-bifunctional cleavable linker, NHS—S—S—PEG₃-azido (Conju-probeInc.), at a 1:3 molar ratio. The product, azido-PEG₃-S—S-fingolimod waspurified by HPLC to remove the excess, unreacted fingolimod molecules.The procedures for conjugation and purification were similar to thosedescribed in the preceding example.

The synthesized azido-PEG₃-S—S-conjugated fingolimod, as illustratedbelow, had a m.w. of 629.33 daltons.

Example 7 Conjugation of Azido-PEG3-S—S-Conjugated Fingolimod Moleculewith a NHS-PEG4-Dibenzylcyclooctyne (DBCO) Crosslinker

Azido-PEG₃-S—S-conjugated fingolimod molecule was dissolved in 100% DMSOat a final concentration of 10 mM, and NHS-PEG₄-DBCO crosslinker wasdissolved in 100% DMSO at a final concentration of 250 mM. 5 μl ofNHS-PEG₄-DBCO crosslinker was added to 400 μl of the dissolvedazido-PEG₃-S—S-conjugated fingolimod solution to a final molar ratio of1/3.2 (NHS-PEG₄-DBCO: azido-PEG₃-S—S-conjugated fingolimod) in 100 mMsodium phosphate buffer at pH 7.5. The reaction mixture was incubatedfor 3 hours at room temperature.

The synthesized NHS-PEG₄-PEG₃-S—S-conjugated fingolimod, as illustratedbelow, had a m.w. of 1,278.61 daltons. The two isotopic peaks were alsovisible in the MS spectrum at 1,279.64 and 1,280.635, corresponding to[M+H+l] and [M+H+2].

Example 8 Conjugation of NHS-PEG₅-Conjugated Fingolimod Molecules toTCO-Peptide 2 and 3

TCO-peptide 2 was dissolved in 100 mM sodium phosphate buffer at pH 7.5to a concentration of 20 mM, and NHS-PEG₅-conjugated fingolimod wasdissolved in 100% DMSO to a concentration of 50 mM. TCO-peptide 2 andNHS-PEG₅-conjugated fingolimod were mixed at 1/42 molar ratio in 100%DMSO and incubated for 3 hours at room temperature. Subsequently,additional TCO-peptide 2 was added to the reaction solution to a finalmolar ratio of 1/13.5 (TCO-peptide 2: NHS PEG₅-conjugated fingolimod) in100% DMSO. The mixture was further incubated for 3 hours at roomtemperature. FIG. 4 shows that the drug bundle of TCO-peptide 2 withfingolimod had a m.w. of 5,069 daltons.

TCO-peptide 3 was dissolved in 100 mM sodium phosphate buffer at pH 7.5to a concentration of 10 mM, and NHS-PEG₅-conjugated fingolimod wasdissolved in 100% DMSO to a concentration of 50 mM. TCO-peptide 3 andPEG₅-NHS-conjugated fingolimod were mixed at 1/42 molar ratio at roomtemperature for overnight. FIG. 5 shows that the drug bundle ofTCO-peptide 3 with fingolimod had a m.w. of 9,479 daltons, indicatingthat ten fingolimod molecules were conjugated to the TCO-peptide 3linker unit.

The synthesized drug bundle, as illustrated below, was composed of alinker unit with a free TCO functional group and a set of fivefingolimod molecules.

The second synthesized drug bundle, as illustrated below, was composedof a linker unit with a free TCO functional group and a set of tenfingolimod molecules.

Example 9 Conjugation of NHS-PEG₅-Conjugated Fingolimod PhosphateMolecules to TCO-Peptide 2

TCO-peptide 2 and NHS-PEG₅-conjugated fingolimod phosphate were mixed at1/42 molar ratio in 100 mM sodium phosphate buffer at pH 7.5 at roomtemperature for 3 hours. Mass spectrometric analysis shows that the drugbundle of TCO-peptide 2 with fingolimod phosphate had a m.w. of 5,379.16daltons (FIG. 6).

The synthesized drug bundle, as illustrated herein, was composed of alinker unit with a free TCO functional group and a set of fivefingolimod phosphate molecules as effector elements.

Example 10 Conjugation of NHS-PEG₄-PEG₃-S—S-Conjugated FingolimodMolecules to TCO-Peptide2

Five NHS-PEG₄-PEG₃-S—S-conjugated fingolimod molecules were attached toTCO-peptide 2. The conjugation of NHS-PEG₄-PEG₃-S—S-conjugatedfingolimod molecules to the NH₂ groups of lysine residues of theTCO-peptide 2 was performed similarly as in the preceding example. Theidentification was carried out by mass spectrometry MALDI-TOF.

The synthesized drug bundle, as illustrated below, had a m.w. of 7,815daltons; it was composed of a linker unit with a free TCO functionalgroup and a set of five fingolimod molecules.

Example 11 Production of Recombinant Ectodomain of Human CD32a byHEK293F Overexpression System

The gene-encoding sequence was placed in pG1K expression cassette. Theamino acid sequence of the extracellular portion of human CD32a, whichwas expressed as a recombinant protein with a histidine-tag, is setforth in SEQ ID NO: 28. Recombinant ectodomain of human CD32a wasexpressed in FreeStyle 293F suspension culture cell expression systemand medium (Invitrogen, Carlsbad, USA). FreeStyle 293F cells were seededat a cell density of 1.0×10⁶ viable cells/ml in 600-ml culture andmaintained for 18 to 24 hours prior to transfection to ensure that thecells were actively dividing at the time of transfection. At the time oftransfection, 1.0×10⁷ cells in a 96-ml medium in a 2-liter Erlenmeyershaker flask were transfected by using linear polyethylenimine with anaverage molecular weight of 25 kDa (Polysciences, Warrington, USA) as atransfection reagent. The transfected cells were incubated at 37° C. for4 hours post-transfection in an orbital shaker (125 rpm), and their celldensity was then adjusted to 2.5×10⁶ cells/ml with a fresh medium andincubated for 4 to 5 days. Culture supernatants were harvested andprotein in the media was purified using nickel affinity chromatography.FIG. 7 shows SDS-PAGE analysis of purified protein of ectodomain ofhuman CD32a.

Example 12 Production of Recombinant Ectodomain of Human Transferrin-1Receptor (TfR) by HEK293F Overexpression System

The gene-encoding sequence was placed in pG1K expression cassette. Theamino acid sequence of the ectodomain of human TfR1, which was expressedas a recombinant protein with a histidine-tag, is set forth in SEQ IDNO: 29. Recombinant ectodomain of human TfR1 was expressed in FreeStyle293F suspension culture cell expression system and medium (Invitrogen,Carlsbad, USA). FreeStyle 293F cells were seeded at a cell density of1.0×10⁶ viable cells/ml in 600-ml culture and maintained for 18 to 24hours prior to transfection to ensure that the cells were activelydividing at the time of transfection. At the time of transfection,1.0×10⁷ cells in 96-ml medium in a 2-liter Erlenmeyer shaker flask weretransfected by using linear polyethylenimine with an average molecularweight of 25 kDa (Polysciences, Warrington, USA) as a transfectionreagent. The transfected cells were incubated at 37° C. for 4 hourspost-transfection in an orbital shaker (125 rpm), and their cell densitywas then adjusted to 2.5×10⁶ cells/m1 with a fresh medium and incubatedfor 4 to 5 days. Culture supernatants were harvested and protein in themedia was purified using nickel affinity chromatography. FIG. 8 showsSDS-PAGE analysis of the purified protein of ectodomain of human TfR1.

Example 13 Production of scFv of mAb Specific for Protein F of RSV, mAbSpecific for Endotoxin, and mAb Specific for Ectodomain of CD32a byExpi293F Overexpression System

The V_(L) and V_(H) of the scFv specific for Protein F of RSV were frommonoclonal antibody palivizumab; the V_(L) and V_(H) of the scFvspecific for endotoxin were from monoclonal antibody WN1 222-5 (U.S.Pat. No. 5,858,728); V_(L) and V_(H) of the scFv specific for ectodomainof CD32a were from MDE-8 (US Patent Application publicationUS2007/0253958). The scFv derived from those antibodies were designed tocontain a flexible linker of GGGGSGGGGS and a terminal cysteine residueat the C-terminus. The cysteine residue provides a sulfhydryl group forconjugation with maleimide group present at the free ends of linkingarms in various linker units. To produce the scFv of mAb specific forProtein F of RSV, mAb specific for endotoxin, and mAb specific forextracellular component of CD32a, the V_(L) and V_(H) DNA sequences ofthe three antibodies with further codon optimization were used. DNAsequences encoding V_(L)-GSTSGSGKPGSGEGSTKG-V_(H)-(GGGGS)₂—C weresynthesized. The amino acid sequences of the scFv of mAb specific forProtein F of RSV, mAb specific for endotoxin, and mAb specific forectodomain of CD32a prepared for the experiments of the invention areset forth in SEQ ID NOs: 30 to 32, respectively.

For preparing scFv proteins using a mammalian expression system, anoverexpression system based on Expi293F™ cell line were used forexperimentation. The system employed ExpiFectamine™ 293 transfection kit(Life Technologies, Carlsbad, USA) consisting of the Expi293F™ cellline, the cationic lipid-based ExpiFectamine™ 293 Reagent andExpiFectamine™ 293 transfection Enhancers 1 and 2, and the medium, whichwas part of the expression system (Gibco, New York, USA).

The scFv-encoding sequence was placed in pG1K expression cassette.Expi293F cells were seeded at a density of 2.0×10⁶ viable cells/ml inExpi293F expression medium and maintained for 18 to 24 hours prior totransfection to ensure that the cells were actively dividing at the timeof transfection. At the time of transfection, 7.5×10⁸ cells in 255 mlmedium in a 2-liter Erlenmeyer shaker flask were transfected byExpiFectamine™ 293 transfection reagent. The transfected cells wereincubated at 37° C. for 16 to 18 hours post-transfection in an orbitalshaker (125 rpm) and the cells were added ExpiFectamine™ 293transfection enhancer 1 and enhancer 2 to the shaker flask, andincubated for 5 to 6 days. Culture supernatants were harvested and scFvproteins in the media were purified using Protein L affinitychromatography.

FIGS. 9A and 9B show SDS-PAGE and ELISA analyses of purified scFv of mAbspecific for Protein F of RSV; FIGS. 9C and 9D show SDS-PAGE and ELISAanalyses of purified scFv of mAb specific for endotoxin; FIGS. 9E and 9Fshow SDS-PAGE and ELISA analyses of purified scFv of mAb specific forectodomain of CD32a. The 96-well ELISA plates (Greiner Bio-one) werecoated with 5 μg/ml of Protein F of RSV, 10 μg/ml of endotoxin, and 5μg/ml of ectodomain of CD32a, respectively. Purified scFvs were detectedby HRP-conjugated protein L at a ratio of 1:5000.

The ELISA results show that each purified scFv protein boundspecifically to its antigen (Protein F of RSV, endotoxin, or ectodomainof TfR1 protein), using adalizumab scFv (anti-TNF-α scFv) as a negativecontrol.

Example 14 Production of scFv of mAb Specific for Ectodomain of TfR1 andmAb Specific for β-Amyloid by Expi293F Overexpression System

The V_(L) and V_(H) of the scFv specific for ectodomain of TfR1 werefrom monoclonal antibody OX26; the V_(L) and V_(H) of the scFv specificfor β-amyloid were from monoclonal antibody bapineuzumab. The scFvderived from those antibodies were designed to contain a flexible linkerof GGGGSGGGGS and a terminal cysteine residue at the C-terminus. Thecysteine residue provides a sulfhydryl group for conjugation withmaleimide group present at the free ends of linking arms in variouslinker units. To produce the scFv of mAb specific for ectodomain of TfR1and mAb specific for -β-amyloid, the V_(L) and V_(H) DNA sequences ofthe two antibodies with further codon optimization were used. DNAsequences encoding V_(L)-GSTSGSGKPGSGEGSTKG-V_(H)-(GGGGS)₂—C weresynthesized. The amino acid sequences of the scFv of mAb specific forectodomain of TfR1 and mAb specific for β-amyloid prepared for theexperiments of the invention are set forth in SEQ ID NOs: 33 and 34,respectively.

For preparing scFv proteins using mammalian expression systems, theoverexpression system based on Expi293F™ cell line were used. The systememployed ExpiFectamine™ 293 transfection kit (Life Technologies,Carlsbad, USA) consisting of the Expi293F™ cell line, the cationiclipid-based ExpiFectamine™ 293 Reagent and ExpiFectamine™ 293transfection Enhancers 1 and 2, and the medium (Gibco, New York, USA).

The scFv-encoding sequence was placed in pG1K expression cassette.Expi293F cells were seeded at a density of 2.0×10⁶ viable cells/ml inExpi293F expression medium and maintained for 18 to 24 hours prior totransfection to ensure that the cells were actively dividing at the timeof transfection. At the time of transfection, 7.5×10⁸ cells in 255 mlmedium in a 2-liter Erlenmeyer shaker flask were transfected byExpiFectamine™ 293 transfection reagent. The transfected cells wereincubated at 37° C. for 16 to 18 hours post-transfection in an orbitalshaker (125 rpm) and the cells were added ExpiFectamine™ 293transfection enhancer 1 and enhancer 2 to the shaker flask, andincubated for 5 to 6 days. Culture supernatants were harvested and scFvproteins in the media were purified using Protein L affinitychromatography. FIGS. 10A and 10B respectively show SDS-PAGE and ELISAanalyses of purified scFv of mAb specific for ectodomain of TfR1. FIGS.10C and 10D respectively show SDS-PAGE and ELISA analyses of purifiedscFv of mAb specific for β-amyloid. The ELISA plates were coated with 5μg/ml of ectodomain of TfR1 and 5 μg/ml of β-amyloid, respectively.Purified scFvs were detected by HRP-conjugated protein L at a ratio of1:5000.

The ELISA results show that each purified scFv protein boundspecifically to its antigen (ectodomain of TfR1 or β-amyloid), usingHRP-conjugated protein L alone as a negative control.

Example 15 Construction and Selection of Phage-Displayed scFvs Specificfor Ectodomain of Human CD32a

The phage clones carrying the scFv specific for the ectodomain of humanCD32a were obtained through a contractual arrangement with Dr. An-SueiYang's laboratory at the Genomics Research Center, Academia Sinica,Taipei, Taiwan. The framework sequence of the GH2 scFv library wasderived from G6 anti-VEGF Fab (Protein Bank Code 2FJG) and cloned intorestriction sites SfiI and NotI of phagemid vector pCANTAB5E (GEHealthcare), carrying an ampicillin resistance, a lacZ promotor, a pelBleader sequence for secretion of scFv fragments into culturesupernatants, a E-tag applicable for detection. The V_(H) and V_(L)domains of the scFv template were diversified separately based on theoligonucleotide-directed mutagenesis procedure; the three CDRs in eachof the variable domains were diversified simultaneously. The scFvlibrary of over 10⁹ clones was used for selections on ectodomain ofCD32a.

Maxisorp 96-well plates (Nunc) coated with recombinant CD32a proteins (1μg/100 μL PBS per well) were used for panning anti-CD32a antibodies. Inbrief, the wells were coated with human CD32a by shaking the coatingsolution in the wells for 2 hours at room temperature. The CD32a-coatedwells were then treated with blocking buffer (5% skim milk in PBST(phosphate buffered saline with 0.1% tween-20)) for 1 hour at roomtemperature. Recombinant phages in the blocking buffer diluted to 8×10¹¹CFU/ml was added to the CD32a-coated wells for 1 hour with gentleshaking; CFU stands for colony-forming unit. The wells were then washedvigorously 10 times with PBST, followed by 6 times with PBS to removenonspecific binding phages. The bound phages were eluted using 0.1 MHCl/glycine buffer at pH 2.2, and the elution solution was neutralizedimmediately by 2 M Tris-base buffer at pH 9.0. E. coli strain ER2738(OD600=˜0.6) was used for phage infection at 37° C. for 30 minutes;non-infected E. coli was eliminated by treating with ampicillin for 30minutes. After ampicillin treatment, helper phage M13KO7 carryingkanamycin resistance was added for another one-hour incubation. Theselected phages rescued by helper phage in the E. coli culture wereamplified with vigorously shaking overnight at 37° C. in the presence ofkanamycin. The amplified phages were precipitated in PEG/NaCl, and thenresuspended in PBS for the next selection-amplification cycles. A totalof three consecutive panning rounds was performed on ectodomain of CD32aby repeating this selection-amplification procedure.

Phage-infected ER2738 colonies of plates with dilution series werecounted and phage titers were calculated, yielding the output titer/ml(CFU/ml) per panning round. A 1000-fold increase in phage output titlefrom 1.6E+04 CFU/well to 2.2E+07 CFU/well was obtained after threerounds of panning. The phage output/input titer ratios from each roundare shown in FIG. 11A. For each panning round, the phage output/inputtiter ratios are given on the y-axis. There was clear enrichment of thepositive clones over the three rounds of panning. The third panninground resulted in a 100-fold on the ratios of phage output/input titerover the first round, as the binding clones became the dominantpopulation in the library.

In a typical selection procedure, after three rounds of antigen-panningon human CD32a-coated wells in ELISA plates, approximately 80% of thebound phage particles bound to CD32a specifically in ELISA with coatedCD32a.

Example 16 Single Colony ELISA Analysis of Phage-Displayed scFvsSpecific for Ectodomain of Human CD32a

E. coli strain ER2738 infected with single-clonal phages each harboringa selected scFv gene in its phagemid was grown in the mid-log phase in2YT broth (16 g/L tryptone, 10 g/L yeast extract, 5 g/L NaCl, pH 7.0)with 100 μg/ml ampicillin in deep well at 37° C. with shaking. Afterbroth reaching an OD600 of 1.0, IPTG was added to a final concentrationof 1 μg/ml. The plates were incubated at 37° C. overnight withrigorously shaking; thereafter, the plates were centrifuged at 4000 gfor 15 minutes at 4° C.

For soluble scFv binding test, ELISA was carried out. In brief, Maxisorp96-well plate (Nunc) was coated with ectodomain of CD32a (0.5 μg/100 μlPBS per well) or a negative control antigen human transferrin-1receptor, for 18 hours with shaking at 4° C. After treated with 300 μlof blocking buffer for 1 hour, 100 μl of secreted scFv in thesupernatant was mixed with 100 μl of blocking buffer and then added tothe coated plate for another 1 hour. Goat anti-E-tag antibody(conjugated with HRP, 1:4000, Cat. No. AB19400, Abcam) was added to theplate for 1 hour. TMB substrate (50 μl per well) was added to the wellsand the absorbance at 450 nm was measured after reactions were stoppedby adding 1N HCl (50 μl per well).

A total of 192 phage clones after the third round of panning weresubjected to the present analysis. Among them, 12 scFv clones that boundto CD32a with a differential of OD450 greater than 10 were furthercharacterized by sequencing genes encoding these scFvs. Six differentDNA sequences were identified. FIG. 11B shows the ELISA result of anscFv clone 22D1. The amino acid sequence of an scFV clone 22D1, whichbinds to human CD32a with an OD450 of 0.8, is shown in SEQ ID NO: 35.

Example 17 Construction and Selection of Phage-Displayed scFvs Specificfor Ectodomain of Human TfR1

The phage clones carrying the scFv specific for the ectodomain of humanTfR1 were obtained through a contractual arrangement with Dr. An-SueiYang's laboratory at the Genomics Research Center, Academia Sinica,Taipei, Taiwan. The framework sequence of the GH2 scFv library wasderived from G6 anti-VEGF Fab (Protein Bank Code 2FJG) and cloned intorestriction sites SfiI and NotI of phagemid vector pCANTAB5E (GEHealthcare), carrying an ampicillin resistance, a lacZ promotor, a pelBleader sequence for secretion of scFv fragments into culturesupernatants, an E-tag applicable for detection. The V_(H) and V_(L)domains of the scFv template were diversified separately based on theoligonucleotide-directed mutagenesis procedure; the three CDRs in eachof the variable domains were diversified simultaneously. The scFvlibrary of over 10⁹ clones was used for selections on ectodomain ofCD32a.

Maxisorp 96-well plates (Nunc) coated with recombinant ectodomain ofTfR1 proteins (1 μg/100 μL PBS per well) were used for panning anti-TfR1antibodies. In brief, the wells were coated with human TfR1 by shakingthe coating solution in the wells for 2 hours at room temperature. TheTfR1-coated wells were then treated with blocking buffer (5% skim milkin PBST (phosphate buffered saline with 0.1% tween-20)) for 1 hour atroom temperature. Recombinant phages in the blocking buffer diluted to8×10¹¹ CFU/ml was added to the TfR1-coated wells for 1 hour with gentleshaking; CFU stands for colony-forming unit. The wells were then washedvigorously 10 times with PBST, followed by 6 times with PBS to removenonspecific binding phages. The bound phages were eluted using 0.1 MHCl/glycine buffer at pH 2.2, and the elution solution was neutralizedimmediately by 2 M Tris-base buffer at pH 9.0. E. coli strain ER2738(0D600=˜0.6) was used for phage infection at 37° C. for 30 minutes;non-infected E. coli was eliminated by treating with ampicillin for 30minutes. After ampicillin treatment, helper phage M13KO7 carryingkanamycin resistance was added for another one-hour incubation. Theselected phages rescued by helper phage in the E. coli culture wereamplified with vigorously shaking overnight at 37° C. in the presence ofkanamycin. The amplified phages were precipitated in PEG/NaCl, and thenresuspended in PBS for the next selection-amplification cycles. A totalof three consecutive panning rounds was performed on ectodomain of TfR1by repeating this selection-amplification procedure.

Phage-infected ER2738 colonies of plates with serial dilutions werecounted and phage titers were calculated, yielding the output titer/ml(CFU/ml) per panning round. A 10⁴-fold increase in phage output titlefrom 3.74E+03 CFU/well to 1.5E+08 CFU/well was obtained after threerounds of panning. The phage output/input titer ratios from each roundare shown in FIG. 12A. For each panning round, the phage output/inputtiter ratios are given on the y-axis. There was clear enrichment of thepositive clones over the three rounds of panning. The third panninground resulted in a 10⁴-fold on the ratios of phage output/input titerover the first round, as the binding clones became the dominantpopulation in the library.

In a typical selection procedure, after three rounds of antigen-panningon human TfR1-coated wells in ELISA plates, approximately 80% of thebound phage particles bound to TfR1 specifically in ELISA with coatedTfR1.

Example 18 Single Colony ELISA Analysis of Phage-Displayed scFvsSpecific for Ectodomain of Human TfR1

E. coli strain ER2738 infected with single-clonal phages each harboringa selected scFv gene in its phagemid was grown in the mid-log phase in2YT broth (16 g/L tryptone, 10 g/L yeast extract, 5 g/L NaCl, pH 7.0)with 100 μg/ml ampicillin in deep well at 37° C. with shaking. Afterbroth reaching an OD600 of 1.0, IPTG was added to a final concentrationof 1 μg/ml. The plates were incubated at 37° C. overnight withrigorously shaking; thereafter, the plates were centrifuged at 4000 gfor 15 minutes at 4° C.

For soluble scFv binding test, ELISA was carried out. In brief, Maxisorp96-well plate (Nunc) was coated with ectodomain of TfR1 (0.5 μg/100 μlPBS per well) or a negative control antigen CD16b, for 18 hours withshaking at 4° C. After treated with 300 μl of blocking buffer for 1hour, 100 μl of secreted scFv in the supernatant was mixed with 100 μlof blocking buffer and then added to the coated plate for anotherone-hour. Goat anti-E-tag antibody (conjugated with HRP, 1:4000, Cat.No. AB19400, Abcam) was added to the plate for 1 hour. TMB substrate (50μl per well) was added to the wells and the absorbance at 450 nm wasmeasured after reactions were stopped by adding 1N HCl (50 μl per well).

A total of 192 phage clones after the third round of panning weresubjected to the present analysis. Among them, 23 scFv clones that boundto TfR1 with a differential of OD450 greater than 10 were furthercharacterized by sequencing the genes encoding these scFvs. Sixteendifferent DNA sequences were identified. FIG. 12B shows the ELISA resultof an scFv clone 12A1. The amino acid sequence of the scFV clone 12A1,which binds to human TfR1 with an OD450 of 1.7, is shown in SEQ ID NO:36.

Example 19 Preparation of TCO-scFv Specific for the Ectodomain of CD32a

The DNA sequence encoding SEQ ID NO: 32 was synthesized and expressed asin the above Examples. For the conjugation with Mal-PEG₃-TCO(Conju-probe, Inc.), the cysteine residue at the C-terminal end of thepurified scFv of anti-CD32a mAb was reduced by incubating with 5 mMdithiothreitol (DTT) at room temperature for 4 hours with gentleshaking. The buffer of reduced scFv proteins were exchanged to sodiumphosphate buffer (100 mM sodium phosphate, pH7.0, 50 mM NaCl, and 5 mMEDTA) by using NAP-10 Sephadex G-25 column. After the reduction reactionand buffer exchange, conjugation was conducted overnight at roomtemperature in a reaction molar ratio of 10:1 ([Mal-PEG₃-TCO:[scFv]].The excess crosslinker was removed by a desalting column and theTCO-conjugated scFv product was analyzed.

The results of mass spectroscopy MALDI-TOF analysis indicated that thesample of TCO-conjugated scFv specific for CD32a had a m.w. of 27,337daltons. The purity of TCO-conjugated scFvs specific for CD32 wasidentified through Coomassie blue staining of 12% SDS-PAGE. FIG. 13A andFIG. 13B show, respectively, the ELISA and Mass spectrometric analysisof TCO-conjugated scFv specific for CD32a, in which unmodified scFvspecific for CD32a was used as a positive control. According to theELISA results, TCO-conjugated scFv specific for CD32a bound torecombinant ectodomain of human CD32a.

Example 20 Preparation of Tetrazine-scFv Specific for the Ectodomain ofTfR1

The DNA sequence encoding SEQ ID NO: 33 was synthesized and expressed asin the above Examples. For the conjugation with Mal-PEG₄-tetrazine(Conju-probe, Inc.), the cysteine residue at the C-terminal end of thepurified scFv of mAb specific for TfR1 was reduced by incubating with 5mM DTT at room temperature for 4 hours with gentle shaking. The bufferof reduced scFv proteins were exchanged to sodium phosphate buffer (100mM sodium phosphate, pH 7.0, 50 mM NaCl, and 5 mM EDTA) by using NAP-10Sephadex G-25 column. After the reduction reaction and buffer exchange,conjugation was conducted overnight at 4° C. in a reaction molar ratioof 10:1 ([Mal-PEG₄-tetrazine:[scFv]]. The excess crosslinker was removedby a desalting column and the tetrazine-conjugated scFv product wasanalyzed.

The results of mass spectroscopy MALDI-TOF analysis indicated that thesample of tetrazine-conjugated scFv specific for TfR1 had a m.w. of27,086 daltons. The purity of tetrazine-conjugated scFv specific forTfR1 was identified through Coomassie blue staining of 12% SDS-PAGE.FIG. 14A and FIG. 14B show, respectively, the ELISA and Massspectrometric analysis of tetrazine-conjugated scFv specific for TfR1,in which unmodified scFv specific for TfR1 was used as a positivecontrol. According to the ELISA results, tetrazine-conjugated scFvspecific for TfR1 bound to recombinant ectodomain of TfR1.

Example 21 Conjugation of Three scFvs Specific for Endotoxin to theThree Maleimide-PEG₁₂ Linking Arms Based on Tetrazine-Peptide 1

This example demonstrates that three scFvs can be conjugated to thethree PEG₁₂-maleimide linking arms based on tetrazine-peptide 1. Priorto conjugation with the tetrazine-peptide 1 that had threePEG₁₂-maleimide linking arms, scFv specific for endotoxin was incubatedwith DTT at a molar ratio of 2:1 ([DTT]:[scFv]) at 25° C. for 4 hourswith gentle shaking to keep its C-terminal cysteine in a reduced form.Subsequently, the buffer of reduced scFv specific endotoxin wasexchanged to maleimide-SH coupling reaction buffer (100 mM sodiumphosphate, pH 7.0, 50 mM NaCl and 5 mM EDTA) by using an NAP-10 SephadexG-25 column (GE Healthcare). After the reduction and buffer exchange,the conjugation to the tetrazine-peptide 1 having three maleimide-PEG₁₂linking arms was conducted overnight at 4° C. at a molar ratio of 1:4([linker]:[Protein]).

The PEG₁₂-maleimide-conjugated tetrazine-peptide 1 conjugated with threescFvs specific for endotoxin was separated from the free scFv, freePEG₁₂-maleimide-conjugated tetrazine-peptide 1 and thePEG₁₂-maleimide-conjugated tetrazine-peptide 1 conjugated with one andtwo scFvs specific for endotoxin by size exclusion chromatography columnS75.

FIG. 15A is the FPLC elution profile on a synthesized targeting linkerunit composed of a linker unit with a free tetrazine functional groupand a set of three scFvs specific for endotoxin as targeting elementswith retention volume of 9.5 ml. The product (i.e., thePEG₁₂-maleimide-conjugated tetrazine-peptide 1 having a free tetrazinefunctional group and being conjugated with a set of three scFvs specificfor endotoxin) was purified in the elution fraction and shown in lane 4(indicated by arrow) of the 10% SDS-PAGE analysis shown in FIG. 15B.

Example 22 Analysis of a Targeting Linker Unit Containing Three scFvsSpecific for Endotoxin Linked to the Three Maleimide-PEG₁₂ Linking ArmsBased on Tetrazine-Peptide 1 by MALDI-TOF

The sample of the targeting linker unit with three scFvs specific forendotoxin linked to the three maleimide-PEG₁₂ linking arms based ontetrazine-peptide 1 was analyzed by MALDI-TOF. The median of theexperimental molecular weight was consistent with the median oftheoretical molecular weight of three scFvs specific for endotoxinconjugated to tetrazine-peptide 1 with three maleimide-PEG₁₂ linkingarms. According to the mass spectrometric profile in FIG. 15C, thepresent targeting linker unit had a median molecular weight of 81,727daltons.

Illustrated below is the synthesized targeting linker unit that wascomposed of a linker unit with a free tetrazine functional group and aset of three scFvs specific for endotoxin as targeting elements.

Example 23 Preparation of a Targeting Linker Unit Based onTetrazine-Peptide 1 with Three scFvs Specific for Protein F of RSV

The conjugation of scFv to the linker unit and the purification andanalysis of the product were the same as in the preceding Examples.

Shown in FIG. 16 is the mass spectrometric analysis of the synthesizedtargeting linker unit that was composed of a linker unit with a freetetrazine functional group and a set of three scFv specific for ProteinF of RSV as targeting elements (illustrated below). As indicated in FIG.16, this effector linker unit had a molecular weight of 81,978 daltons.

Example 24 Conjugation of Three scFvs Specific for β-Amyloid to ThreeMaleimide-PEG₁₂ Linking Arms Based on TCO-Peptide 1

This example was performed to demonstrate that three scFvs could beconjugated to the three maleimide-PEG₁₂ linking arms based onTCO-peptide 1. Prior to conjugation with the TCO-peptide 1 that hadthree maleimide-PEG₁₂ linking arms, scFv specific for 3-amyloid wasincubated with DTT at a molar ratio of 2:1 ([DTT]:[scFv]) at roomtemperature for 4 hours with gentle shaking to keep its C-terminalcysteine in a reduced form. Subsequently, the buffer of reduced scFvspecific for β-amyloid was exchanged to maleimide-SH coupling reactionbuffer (100 mM sodium phosphate, pH 7.0, 50 mM NaCl and 5 mM EDTA) byusing an NAP-10 Sephadex G-25 column (GE Healthcare). After thereduction and buffer exchange, the conjugation to the TCO-peptide 1having three maleimide-PEG₁₂ linking arms was conducted overnight atroom temperature at a molar ratio of 1:4 ([linker]:[Protein]).

The reaction mixture of the preceding examples was adjusted to pH 5.0and then applied to pre-equilibrated (5 mM EDTA, and 50 mM sodiumacetate at pH 5.0) cation exchange column SP Sepharose FF (GEHealthcare). The maleimide-PEG₁₂-conjugated TCO-peptide 1 conjugatedwith three scFvs specific for β-amyloid was eluted using a lineargradient of 0-500 mM sodium chloride in a flow rate of 0.5 ml/min for100 minutes. The maleimide-PEG₁₂-conjugated TCO-peptide 1 conjugatedwith three scFvs specific for β-amyloid was separated from the freescFv, free maleimide-PEG₁₂-conjugated TCO-peptide 1 and themaleimide-PEG₁₂-conjugated TCO-peptide 1 conjugated with one and twoscFvs specific for β-amyloid by cation exchange column SP Sepharose FF.The purified product, maleimide-PEG₁₂-conjugated TCO-peptide 1conjugated with three scFvs specific for β-amyloid, was concentrated andbuffer-exchange into click reaction buffer, 100 mM potassium phosphateat pH 7.0.

FIG. 17A is the FPLC elution profile of cation exchange column SPSepharose FF on a synthesized effector linker unit composed of a linkerunit with a free TCO functional group and a set of three scFvs specificfor β-amyloid as effector elements. Symbol #1 and #2 respectivelyrepresented the eluted peaks of maleimide-PEG₁₂-conjugated TCO-peptide 1conjugated with two scFvs and three scFvs specific for β-amyloid. Theproduct, the maleimide-PEG₁₂-conjugated TCO-peptide 1 bearing a free TCOfunctional group and three scFvs specific for β-amyloid was purified andrevealed in lane 2 of the 8% SDS-PAGE analysis shown in FIG. 17B.

Example 25 Analysis of an Effector Linker Unit Containing Three scFvsSpecific for β-Amyloid Linked to the Three Maleimide-PEG₁₂ Linking ArmsBased on TCO-Peptide 1 by MALDI-TOF

The sample of the targeting linker unit of three scFvs specific forβ-amyloid linked to the three maleimide-PEG₁₂ linking arms based onTCO-peptide 1 was analyzed by MALDI-TOF. The median of the experimentalmolecular weight was consistent with the median of theoretical molecularweight of three scFvs specific for 3-amyloid conjugated to TCO-peptide 1with three maleimide-PEG₁₂ linking arms. According to the massspectrometric profile in FIG. 17C, the synthesized targeting linker unithad the median molecular

Illustrated herein is the synthesized targeting linker unit that wascomposed of a linker unit with a free TCO functional group and a set ofthree scFvs specific for β-amyloid as targeting elements.

Example 26 Preparation of Molecular Construct with Three scFvs Specificfor Protein F of RSV as Targeting Elements and One scFv Specific forEctodomain of CD32a as an Effector Element

In this example, the targeting linker unit of the preceding examples anda TCO-scFv specific for extodomain of CD32a were coupled via atetrazine-TCO iEDDA reaction. Specifically, the targeting linker unithad three scFv specific for Protein F of RSV and one free tetrazinegroup.

The procedure for tetrazine-TCO ligation was performed per themanufacturer's instructions (Jena Bioscience GmbH, Jena, Germany).Briefly, 100 μl of the targeting linker unit (0.3 mg/ml) was added tothe solution containing the effector element at a molar ratio of 1:1.2([tetrazine]:[TCO]). The reaction mixture was incubated for 1 hour atroom temperature. The product was subjected to mass spectrometricanalysis, and the result indicated a molecular weight of 113,036 daltons(FIG. 18A).

The product, a single linker unit molecular construct with three scFvsspecific for Protein F of RSV as targeting elements and one scFvspecific for ectodomain of CD32a as an effector element, is illustratedherein.

Example 27 Preparation of Molecular Construct with Three scFvs Specificfor Endotoxin as Targeting Elements and One scFv Specific for Ectodomainof CD32a as an Effector Element

The targeting linker unit prepared in an earlier Example and theTCO-scFv specific for ectodomain of CD32a were coupled via atetrazine-TCO iEDDA reaction.

The procedure for tetrazine-TCO ligation was performed as described inthe previous Example. The product, as illustrated below, was a singlelinker unit molecular construct with three scFvs specific for endotoxinas targeting elements and one scFv specific for ectodomain of CD32a asan effector element. The mass spectrometric analysis shown in FIG. 18Bindicated that this molecular construct had a molecular weight of113,761 daltons.

Example 28 Preparation of Molecular Construct with One scFv Specific forEctodomain of TfR1 as a Targeting Element and Three scFvs Specific forβ-Amyloid as Effector Elements

The targeting linker unit prepared in an earlier Example and thetetrazine-scFv specific for ectodomain of TfR1 were coupled via atetrazine-TCO iEDDA reaction.

The procedure for tetrazine-TCO ligation was performed per themanufacturer's instructions (Jena Bioscience GmbH, Jena, Germany).Briefly, 12.6 μl of the targeting element (5.65 mg/ml) was added to thesolution containing the linker unit with effector elements at a molarratio of 10:1 ([tetrazine]:[TCO]). The reaction mixture was incubatedfor 3 hours at room temperature. The product was subjected to massspectrometric analysis, and the result indicated a molecular weight of114,248 daltons (FIG. 18C).

The product, as illustrated herein, was a single linker unit molecularconstruct with one scFv specific for ectodomain of TfR1 as a targetingelement and three scFvs specific for β-amyloid as effector elements.

It will be understood that the above description of embodiments is givenby way of example only and that various modifications may be made bythose with ordinary skill in the art. The above specification, examplesand data provide a complete description of the structure and use ofexemplary embodiments of the invention. Although various embodiments ofthe invention have been described above with a certain degree ofparticularity, or with reference to one or more individual embodiments,those with ordinary skill in the art could make numerous alterations tothe disclosed embodiments without departing from the spirit or scope ofthis invention.

What is claimed is:
 1. A linker unit comprising, a center core thatcomprises, (1) a first polypeptide comprising a plurality of lysine (K)residues, wherein each K residue and its next K residue are separated bya filler sequence comprising glycine (G) and serine (S) residues, andthe number of K residues ranges from 2 to 15; or (2) a secondpolypeptide comprising the sequence of (X_(aa)—K)_(n), where X_(aa) is aPEGylated amino acid having 2 to 12 repeats of ethylene glycol (EG)unit, and n is an integral from 2 to 15; wherein at least one of the N-and C-terminal amino acid residues of the center core is an amino acidhaving an azide or an alkyne group or is a cysteine residue, whereinwhen one of the N- and C-terminal amino acid residues is the cysteineresidue, the linker unit further comprises, optionally, a coupling armthat is linked to the cysteine residue via the thiol group of thecysteine residue and has the azide, the alkyne, a tetrazine, acyclooctene, or a cyclooctyne group at the free terminus thereof, aplurality of linking arms respectively linked to the K residues of thecenter core; optionally, a plurality of connecting arms respectivelylinked to the plurality of the linking arms via CuAAC reaction, SPAACreaction, or iEDDA reaction; and a plurality of first elements that arerespectively linked to the plurality of linking arms via forming anamide bound therebetween, or via thiol-maleimide reaction, CuAACreaction, SPAAC reaction, or iEDDA reaction; or respectively linked tothe plurality of connecting arms via forming an amide boundtherebetween, or via thiol-maleimide reaction, wherein, each of thefirst elements is a single-chain variable fragment (scFv) specific for aviral protein or a bacterial protein; and when the plurality of linkingarms are linked to the plurality of connecting arms or the plurality offirst elements via CuAAC reaction or SPAAC reaction, then the amino acidresidue at the N- or C-terminus of the center core is a cysteineresidue, and the free terminus of the coupling arm is the tetrazine orthe cyclooctene group; or when the plurality of linking arms are linkedto the plurality of connecting arms or the plurality of first elementsvia iEDDA reaction, then the amino acid residue at the N- or C-terminusof the center core has the azide or the alkyne group, or the amino acidresidue at the N- or C-terminus of the center core is a cysteineresidue, and the free terminus of the coupling arm is the azide, thealkyne, or the cyclooctyne group.
 2. The linker unit of claim 1, whereinthe filler sequence has the sequence of GS, GGS, GSG, or SEQ ID NOs:1-16.
 3. The linker unit of claim 1, wherein the first polypeptidecomprises 2-15 units of the sequence of G₁₋₅SK.
 4. The linker unit ofclaim 3, wherein the first polypeptide comprises the sequence of(GSK)₂₋₁₅.
 5. The linker unit of claim 1, wherein each of the linkingarms is a PEG chain having 2-20 repeats of EG units.
 6. The linker unitof claim 1, wherein each of the linking arms is a PEG chain having 2-20repeats of EG units with a disulfide linkage at the free terminusthereof.
 7. The linker unit of claim 1, wherein the coupling arm is aPEG chain having 2-12 repeats of EG units.
 8. The linker unit of claim1, wherein the amino acid residue having the azide group isL-azidohomoalanine (AHA), 4-azido-L-phenylalanine,4-azido-D-phenylalanine, 3-azido-L-alanine, 3-azido-D-alanine,4-azido-L-homoalanine, 4-azido-D-homoalanine, 5-azido-L-ornithine,5-azido-d-ornithine, 6-azido-L-lysine, or 6-azido-D-lysine.
 9. Thelinker unit of claim 1, wherein the amino acid residue having the alkynegroup is L-homopropargylglycine (L-HPG), D-homopropargylglycine (D-HPG),or beta-homopropargylglycine (β-HPG).
 10. The linker unit of claim 1,wherein the cyclooctene group is trans-cyclooctene (TCO); and thecyclooctyne group is dibenzocyclooctyne (DBCO), difluorinatedcyclooctyne (DIFO), bicyclononyne (BCN), or dibenzocyclooctyne (DICO).11. The linker unit of claim 1, wherein the tetrazine group is1,2,3,4-tetrazine, 1,2,3,5-tetrazine or 1,2,4,5-tetrazine, orderivatives thereof.
 12. The linker unit of claim 1, wherein the viralprotein is F protein of respiratory syncytia virus (RSV), gp120 proteinof human immunodeficiency virus type 1 (HIV-1), hemagglutinin A (HA)protein of influenza A virus, or glycoprotein of cytomegalovirus. 13.The linker unit of claim 1, wherein the bacterial protein is endotoxinof Gram(−) bacteria, surface antigen of Clostridium difficile,lipoteichoic acid of Saphylococcus aureus, anthrax toxin of Bacillusanthracis, or Shiga-like toxin type I or II of Escherichia coli.
 14. Thelinker unit of claim 1, further comprising a second element that islinked to the center core via any of the following reactions: CuAACreaction occurred between the azide or alkyne group and the secondelement; SPAAC reaction occurred between the azide or cyclooctyne groupand the second element; and iEDDA reaction occurred between thecyclooctene or tetrazine group and the second element.
 15. The linkerunit of claim 14, wherein the first element is the scFv specific for theviral protein or the bacterial protein, and the second element is anscFv specific for CD32 or CD16b.
 16. The linker unit of claim 15,wherein, the plurality of first elements that are respectively linked tothe plurality of linking arms via forming the amide bound therebetweenor via thiol-maleimide reaction, and the second element is linked to theazide or alkyne group of the N- or C-terminal amino acid residues of thecenter core via CuAAC reaction.
 17. The linker unit of claim 16, furthercomprising a third element that is linked to the coupling arm via iEDDAreaction.
 18. The linker unit of claim 15, wherein, the plurality offirst elements that are respectively linked to the plurality of linkingarms via forming the amide bound therebetween or via thiol-maleimidereaction, and the second element is linked to the azide group of the N-or C-terminal amino acid residues of the center core via SPARC reaction.19. The linker unit of claim 18, further comprising a third element thatis linked to the coupling arm via iEDDA reaction.
 20. A method fortreating an infectious disease in a subject in need thereof, comprisingadministering to the subject a therapeutically effective amount of thelinker unit of claim
 15. 21. The method of claim 20, wherein the viralprotein is F protein of respiratory syncytia virus (RSV), gp120 proteinof human deficiency virus type 1 (HIV-1), hemagglutinin A (HA) proteinof influenza A virus, or glycoprotein of cytomegalovirus.
 22. The methodof claim 20, wherein the bacterial protein is endotoxin of Gram(−)bacteria, surface antigen of Clostridium difficile, lipoteichoic acid ofstaphylococcus aureus, anthrax toxin of Bacillus anthracis, orShiga-like toxin type I or II of Escherichia coli.